Why is GHK-Cu blue?

The color comes from the copper. GHK binds a copper(II) ion, and copper(II) complexes absorb light at the red end of the spectrum, so the powder and its solutions look blue. Bare GHK, without copper, is white. A blue lyophilized cake is a quick visual cue that you have the copper-bound form, though it doesn’t confirm purity or quantity.

Molecular weight is a better check. Bare GHK is about 340 g/mol, the copper complex is about 400 g/mol, and salt forms add weight, so listings from different suppliers can disagree. Confirm the form and mass on the lot report in our COA library before you compare data between sources. Then shop GHK Cu with the lot details in hand.