The Colours of Hydrogen Explained: Green, Blue, Grey and More

Hydrogen is often described as a key part of the energy transition. But if you have been reading about hydrogen, you may have noticed that it comes in a surprising range of colours: green, blue, grey, pink, turquoise and even white.

So, what do the colours of hydrogen actually mean?

The short answer is that hydrogen itself is a colourless gas. The colour refers to the way it is produced and, broadly, the emissions associated with that production process.

Understanding these different production pathways helps explain why some forms of hydrogen are considered lower emissions than others, and why renewable hydrogen is attracting increasing attention in Australia and around the world.

What is hydrogen?

Hydrogen is the lightest element and, in its pure form, is a colourless gas. Unlike fossil fuels, hydrogen does not occur abundantly as a standalone gas on Earth. It is usually found combined with other elements, including in water and hydrocarbons.

To use hydrogen as an energy carrier or industrial feedstock, it needs to be separated from those compounds.

There are several ways to do this. The energy source and technology used to produce hydrogen determine its emissions profile.

This is where the different "colours" of hydrogen come in.

It is important to remember that these colours are industry terminology rather than physical properties of the hydrogen itself. The same hydrogen molecule is produced regardless of whether it is described as green, grey or blue. What changes is how that hydrogen was made.

Hydrogen colours at a glance

The terminology can vary between organisations and countries, so the production pathway and emissions intensity are ultimately more important than the colour alone.

Green hydrogen

Green hydrogen is produced by electrolysis, a process that uses electricity to split water into hydrogen and oxygen.

When the electricity used by the electrolyser comes from renewable sources such as wind or solar, the resulting hydrogen can be produced with very low greenhouse gas emissions.

This is why green hydrogen is often referred to as renewable hydrogen.

The basic process is:

Renewable electricity + water → hydrogen + oxygen

The environmental performance of green hydrogen depends on the electricity used, as well as the wider lifecycle of the equipment, water and infrastructure involved. For this reason, it is more accurate to describe renewable hydrogen as a low-emissions pathway rather than assume that every project has zero emissions across its entire lifecycle.

Green hydrogen is particularly relevant to sectors where direct electrification can be difficult, including some heavy industrial processes, chemicals and long-distance transport applications.

Australia has identified renewable hydrogen as a priority area for industry development. Its 2024 National Hydrogen Strategy focuses on accelerating a clean hydrogen industry and improving the cost competitiveness of renewable hydrogen.

Blue hydrogen

Blue hydrogen is generally produced from natural gas using processes such as steam methane reforming or autothermal reforming.

These processes produce hydrogen as well as carbon dioxide.

The difference between blue and grey hydrogen is that blue hydrogen incorporates carbon capture and storage (CCS) to capture and store some of the carbon dioxide generated during production.

The intention is to reduce the amount of carbon dioxide released into the atmosphere.

However, carbon capture does not necessarily eliminate all greenhouse gas emissions associated with the production pathway. Emissions can occur during the production and processing of natural gas, during hydrogen production and from carbon dioxide that is not captured.

As a result, the emissions intensity of blue hydrogen depends on factors including the technology used, capture rates, energy requirements and upstream emissions.

Grey hydrogen

Grey hydrogen is typically produced from natural gas through steam methane reforming, without carbon capture.

The process separates hydrogen from the natural gas, producing carbon dioxide as a by-product.

Because the resulting carbon dioxide is released into the atmosphere, grey hydrogen has a significantly higher emissions profile than hydrogen produced using renewable electricity.

Grey hydrogen has historically been widely used in industrial applications, particularly where hydrogen is required as a chemical feedstock.

The distinction between grey and blue hydrogen therefore comes down primarily to what happens to the carbon dioxide produced during the process.

Black and brown hydrogen

Black and brown hydrogen are produced from coal.

Both generally use gasification, in which coal is converted into a mixture of gases from which hydrogen can be separated.

The terminology usually distinguishes between the type of coal used:

• Black hydrogen is associated with black coal.
• Brown hydrogen is associated with brown coal or lignite.

Without carbon capture, these production pathways are associated with significant greenhouse gas emissions.

They are therefore generally at the higher-emissions end of the hydrogen production spectrum.

Turquoise hydrogen

Turquoise hydrogen is produced using methane pyrolysis.

Instead of converting methane into hydrogen and carbon dioxide through conventional reforming, methane is heated and separated into hydrogen and solid carbon.

The simplified process is:

Methane + heat → hydrogen + solid carbon

Because the carbon can remain in a solid form rather than being released directly as carbon dioxide, methane pyrolysis has attracted interest as a potential lower-emissions production pathway.

However, turquoise hydrogen is still an emerging technology.

Its overall emissions profile depends on factors such as the source of the methane, the energy used to drive the process, the efficiency of the technology and what happens to the resulting solid carbon.

As with blue hydrogen, looking at the complete production pathway is more useful than relying on the colour alone.

Pink hydrogen

Pink hydrogen is generally used to describe hydrogen produced through electrolysis using nuclear-generated electricity.

The electrolyser splits water into hydrogen and oxygen, but the electricity powering the process comes from nuclear energy rather than renewable sources such as wind or solar.

Some sources also use terms such as red or purple hydrogen for hydrogen produced using nuclear energy, although terminology is not consistent across the industry.

The emissions profile of nuclear-powered hydrogen depends on the specific electricity source and the lifecycle emissions associated with the technology.

Yellow hydrogen

Yellow hydrogen is another term whose meaning can vary.

It is commonly used to describe hydrogen produced through electrolysis using solar electricity.

Under this definition, yellow hydrogen is closely related to green hydrogen because both use electrolysis and renewable electricity. The distinction is that "yellow" specifically identifies solar power as the electricity source.

Because colour terminology is not standardised globally, it is useful to check how an organisation is defining the term before comparing different hydrogen projects.

White hydrogen

White hydrogen refers to naturally occurring geological hydrogen found underground.

Unlike most manufactured forms of hydrogen, white hydrogen does not need to be produced by splitting water or processing fossil fuels. Instead, it may occur naturally through geological processes.

Interest in naturally occurring hydrogen has increased in recent years, but the sector is still developing and questions remain around exploration, extraction, commercial viability, resource availability and environmental impacts.

For that reason, white hydrogen should be viewed as an emerging area rather than an established large-scale source of hydrogen.

Which colour of hydrogen is the cleanest?

There is no single answer based on colour alone.

In general, hydrogen produced using renewable electricity and water through electrolysis can have a very low emissions intensity, which is why green or renewable hydrogen is a major focus of the energy transition.

However, the emissions associated with any hydrogen project need to be assessed across its production pathway and, where relevant, its broader lifecycle.

For example, the emissions profile of blue hydrogen depends on factors including the amount of carbon dioxide captured and stored and the emissions associated with producing and transporting natural gas.

Similarly, the environmental performance of renewable hydrogen depends on factors including the source of electricity and the infrastructure used to produce it.

This is why increasingly, policymakers and industry are focusing not only on hydrogen's colour, but on measurable emissions intensity and the specific production pathway.

Why does low-emissions hydrogen matter?

Hydrogen is already an important industrial commodity, particularly in refining and chemical production.

The opportunity now is to increase the use of low-emissions hydrogen in applications where alternatives are more difficult, costly or technically challenging.

Potential applications include:

• heavy industry
• chemicals and fertiliser production
• green metals
• long-distance transport
• shipping
• aviation fuels and hydrogen-derived fuels
• energy storage
• industrial heat

The International Energy Agency reports that global hydrogen demand surpassed 100 million tonnes in 2025. At the same time, low-emissions hydrogen production remains a small share of total global production, despite continued growth in projects and investment.

This highlights both the opportunity and the challenge facing the industry: scaling low-emissions hydrogen while improving costs, infrastructure, demand and project certainty.

Why is hydrogen important for Australia?

Australia has several advantages for developing a hydrogen industry, including abundant renewable energy resources, available land and an established energy and resources sector.

The Australian Government's National Hydrogen Strategy 2024 sets out a framework for developing hydrogen production, domestic use and exports, with a particular focus on accelerating clean hydrogen and improving its global cost competitiveness.

The strategy identifies opportunities to use hydrogen in areas including:

• green metals
• heavy transport
• shipping and aviation
• chemicals
• energy storage
• low-emissions fuels
• hydrogen-based exports

Australia's renewable resources also create opportunities to produce renewable hydrogen and hydrogen-derived products using wind and solar generation.

The Australian Government is supporting the development of the industry through measures including the Hydrogen Production Tax Incentive and the expanded Hydrogen Headstart Program, which are designed to help improve the economics of renewable hydrogen projects and encourage investment at scale.

What does the future of hydrogen look like?

The hydrogen industry is developing rapidly, but it is still at an early stage.

The International Energy Agency reports that low-emissions hydrogen production grew in 2025 and is expected to continue growing in 2026. However, fossil fuels still dominate global hydrogen production, while high costs, uncertain demand, infrastructure requirements and regulatory issues continue to affect the development of new low-emissions projects.

This means the transition to low-emissions hydrogen will not happen overnight.

Scaling the industry will require investment across the entire hydrogen value chain — from renewable electricity generation and electrolysers to storage, transport, distribution and end-use applications.

For Australia, the combination of renewable energy resources and an established industrial base creates an opportunity to participate in this emerging industry.

Frequently asked questions about hydrogen colours

What is green hydrogen?

Green hydrogen is hydrogen produced by splitting water through electrolysis using renewable electricity, such as electricity generated from wind or solar power.

What is blue hydrogen?

Blue hydrogen is generally produced from natural gas, with carbon capture and storage used to capture and store some of the carbon dioxide generated during production.

What is grey hydrogen?

Grey hydrogen is generally produced from natural gas without carbon capture, meaning the carbon dioxide generated during production is released into the atmosphere.

What is the difference between green and blue hydrogen?

The main difference is the production pathway. Green hydrogen uses electrolysis powered by renewable electricity, while blue hydrogen is generally produced from natural gas with carbon capture and storage.

Which hydrogen is the cleanest?

Green or renewable hydrogen can have a very low emissions intensity when produced using renewable electricity. However, the environmental performance of any hydrogen project should be assessed based on its specific production process and lifecycle emissions rather than its colour alone.

Is hydrogen a renewable energy source?

Hydrogen is better described as an energy carrier rather than a primary energy source. Its environmental impact depends largely on how it is produced.

Hydrogen produced using renewable electricity can be a renewable energy carrier, while hydrogen produced from fossil fuels without emissions controls is not renewable.

Why are there different colours of hydrogen?

The colours are used as shorthand to distinguish different hydrogen production methods and their associated emissions profiles. However, the terminology is not completely standardised, so it is important to look at the underlying technology and emissions intensity.

Why is green hydrogen important for Australia?

Australia has significant renewable energy resources that can support the production of renewable hydrogen. The Australian Government's 2024 National Hydrogen Strategy identifies renewable hydrogen as a priority area for developing a competitive domestic industry and international export opportunities.

From green to blue and beyond: understanding hydrogen's colours

The different colours of hydrogen provide a useful way to understand how hydrogen can be produced — but they are only the starting point.

As the industry develops, the focus is increasingly moving towards the actual emissions intensity, technology, energy source and lifecycle impacts behind each project.

For Australia, renewable hydrogen represents an opportunity to combine the country's renewable energy resources with its industrial and infrastructure capabilities to help decarbonise sectors where direct electrification can be challenging.

At ACCIONA, we are committed to developing infrastructure that supports the transition towards a more sustainable energy system, including renewable energy and the emerging opportunities associated with green hydrogen.

As the hydrogen industry evolves, understanding how hydrogen is produced will remain essential to understanding its role in the energy transition.