The hydrogen economy operates through color-coded classification systems distinguishing production methods & environmental impacts. Grey hydrogen, dominating 95% of global production, generates substantial CO₂ emissions through fossil fuel-based steam methane reforming. Blue hydrogen reduces emissions 85-90% through carbon capture & storage, yet costs approximately 100-200% more than grey hydrogen. Green hydrogen, powered through renewable electricity, achieves zero direct emissions & increasingly competitive costs as renewable electricity prices decline, representing ultimate sustainability objective regarding hydrogen economy development & decarbonization pathways.