Hydrogen has many colors - depending on the type of production: Green - Electricity from renewable energies is used for the electrolysis of water. Grey - Fossil fuels are used for production, the resulting CO2 enters the atmosphere unused. Blue - Fossil fuels are used for production, resulting CO2 is stored. Turquoise - In the methane pyrolysis process, solid carbon is produced instead of CO2 and binds CO2 permanently.