In peptide research, synergy matters. Some compounds may offer greater insight when studied together, and GHK Cu and AHK Cu are two peptides drawing attention for that reason. Different biological pathways Distinct 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 RCSB PDB 6QUG: GHK tagged MBP Nup98(1 29) GHK Cu Engage Peptides