Green hydrogen is commonly produced using renewable energy to electrolyse water into hydrogen and oxygen.
Blue hydrogen is the low-carbon version of grey, black or brown where CO2 is captured.
Pink/purple hydrogen is produced from a low-carbon nuclear power source and is likely to play a significant longer-term role.
Turquoise hydrogen refers to emerging processes, such as pyrolysis of methane, where solid carbon is removed, not CO2.
Yellow hydrogen is produced from the current grid through electrolysers using renewable or conventional power.
Grey hydrogen, the current production technology, involves reforming of hydrocarbon gas in a CO2-intensive process.
Black and brown hydrogen are produced by reforming or gasifying oil and coal, another CO2-intensive process.
White hydrogen is recovered from geological sources and it could make a small contribution.