Blue
Blue H2 is produced from fossil fuels with carbon sequestration
Grey
Grey H2 is produced from fossil fuels and typically uses the methane steam reforming (SMR) process
Black Brown
Black or brown H2 is produced from coal
Turquoise
Turquoise H2 is obtained by the thermal cracking (‘pyrolysis’) of methane
Purple, Pink, Red
Purple, Pink and Red H2 are obtained by using nuclear power.
White
White H2 is naturally occurring hydrogen
Green
Green H2 is produced by water electrolysis using renewable electricity (wind, hydro, etc)