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 Theoretical study of copper binding to GHK peptide ScienceDirect Molecular crystal structure of the tripeptide GHK Cu. In solution, Download Scientific Diagram Interplay of the CuCu distance and coordination geometry as a factor affecting the quantum efficiency in dimeric copper(i) halide complexes with derivatives of 4 pyrazolylpyrimidine 2 thiol Dalton Transactions (RSC Publishing)