Copper tripeptide acetate (GHK Cu acetate) Tripeptide MedChemExpress Your copper peptide product should be this exact blue. If it isn't, you already have your answer. GHK Cu is blue because of coordination chemistry, not dye. The Cu ion at the center GHK Cu Copper Peptide IUCr) The copper(II) binding tripeptide GHK, a valuable crystallization and phasing tag for macromolecular crystallography