Green, Blue and Grey Hydrogen: What the Colours Actually Mean

Hydrogen is a colourless gas. The colour labels describe the production route and, by implication, the emissions associated with it. The shorthand is useful, and it hides variations that matter enormously.

Grey: the incumbent

Most hydrogen produced globally today is grey, made by steam methane reforming.

Natural gas reacts with high-temperature steam to produce hydrogen and carbon monoxide, which then reacts with more steam to produce additional hydrogen and carbon dioxide. The carbon dioxide is released to the atmosphere.

Grey hydrogen is not a fringe product. It is a major industrial commodity, used at enormous scale in:

• Ammonia production for fertiliser.
• Oil refining, for removing sulphur and upgrading heavy fractions.
• Methanol and other chemicals.

Producing a kilogram of grey hydrogen typically releases somewhere around nine to twelve kilograms of carbon dioxide. Multiplied across global production, this is a substantial emissions source — and it exists before anyone proposes new hydrogen applications.

That is the crucial framing: decarbonising existing hydrogen demand is a large, concrete opportunity that requires no new markets at all.

Blue: the same process, with capture

Blue hydrogen uses steam methane reforming or autothermal reforming, with carbon capture attached. The carbon dioxide is captured and stored geologically rather than released.

Its climate credentials rest on two variables, and both are frequently glossed over.

Capture rate. Not all carbon dioxide is captured. Rates vary considerably by process design and by which streams are treated. A plant capturing a high share is a genuinely different product from one capturing a modest share, yet both may be described as blue.

Upstream methane leakage. Natural gas is mostly methane, a far more potent greenhouse gas than carbon dioxide over shorter timescales. Leakage during extraction, processing and transport adds emissions that carbon capture at the plant does nothing to address.

The honest position: blue hydrogen with high capture rates and a tightly controlled gas supply chain delivers a real reduction against grey. Blue hydrogen with moderate capture and leaky upstream supply delivers considerably less than the label implies. The colour alone tells you almost nothing.

Green: electrolysis with renewable power

Green hydrogen is made by splitting water using renewable electricity. Inputs are water and electricity; outputs are hydrogen and oxygen. No direct carbon emissions.

Its challenge is cost. It requires substantial renewable electricity — roughly 50 to 55 kilowatt-hours per kilogram in a real system — and capital-intensive electrolysers that need high utilisation to be economic. We set out the mechanics in what is green hydrogen.

This is precisely why the Gulf features so heavily in green hydrogen planning: the region produces some of the world's cheapest renewable electricity, and electricity cost dominates green hydrogen economics.

The other colours

• Turquoise — methane pyrolysis, splitting methane into hydrogen and solid carbon rather than carbon dioxide. Solid carbon is easier to handle than gas, but the process is early-stage.
• Pink or purple — electrolysis powered by nuclear electricity. Zero-carbon and capable of very high utilisation, since nuclear runs continuously.
• White — naturally occurring geological hydrogen, which has attracted genuine exploration interest.

Why the colour system is being abandoned

Regulators have largely concluded that colours are too crude, and they are right.

The reason is illustrated by a simple comparison: green hydrogen made with electricity from a grid that is only partly renewable may have higher emissions than blue hydrogen with excellent capture rates. Yet one carries the favourable label and the other does not.

So regulation increasingly specifies measured carbon intensity — kilograms of carbon dioxide equivalent per kilogram of hydrogen — with thresholds for support eligibility. Some frameworks add requirements on the electricity used, such as additionality, geographic correlation and temporal matching, to prevent a producer claiming green credentials while drawing from a fossil-heavy grid.

This is more complex and considerably more honest.

What to ask instead of the colour

• What is the measured carbon intensity per kilogram?
• For blue: what capture rate is achieved, and verified by whom?
• For blue: what upstream methane intensity does the gas supply carry?
• For green: what electricity is used, and is it genuinely matched in time and location?
• Does the product meet the regulatory threshold in the intended market?

That last question is increasingly commercially decisive. A producer whose hydrogen fails to qualify under a destination market's carbon intensity rules cannot sell into its support schemes, regardless of what colour it calls itself.

The bottom line

The colours are useful shorthand and inadequate as standards. Grey is the incumbent and the obvious decarbonisation target. Blue's value depends on capture rate and methane discipline. Green is clean and expensive, and its economics live or die on cheap renewable electricity. Carbon intensity is the number that matters.

Follow the hydrogen story with the numbers attached

Hydrogen claims deserve scrutiny, and the useful detail is rarely in the announcement.

• Read energy insights for explainers behind the terminology.
• Explore our Middle East coverage, where the region's hydrogen ambitions are concentrated.
• Subscribe to The Energy Edit — free, independent reporting. Start here.

Hydrogen developers, technology providers and offtakers: explore partnership with Arcnex Energy.