Name the change first
If you're looking at a dark mark, a claim about smoother skin may miss the point. “Bright” doesn't tell you which change a product is meant to make. We'd rather ask what you mean than assume lighter skin is the goal.
Skin relies in part on collagen for strength. Collagen is a protein. Melanin is a pigment that contributes to skin colour. A finding about one doesn't automatically answer a question about the other, even when both turn up in the same skincare conversation.
What do the cream studies say?
A review of copper-peptide research reports less patchy pigmentation among the appearance changes in small cream studies. That's the review's account of older work. Some of those reports weren't full medical-journal papers, so there are limits to how closely we can check them.
A later review of topical GHK also points to the shortage of strong human studies. Taken together, these are reasons to keep reading, rather than a settled answer about fading dark marks. They don't establish what a particular cream will do for your skin.
The pigment experiment has a catch
One laboratory study found more pigment after testing a related copper-peptide mixture. The researchers used a modified form called palmitoyl copper peptide, combined with acetyl tyrosine. They tested it in human and mouse melanoma cell lines: cells grown in a lab, not people's skin.
That ingredient detail matters. The study didn't test ordinary GHK-Cu alone, and it can't show that a GHK-Cu cream causes dark spots. Nor does it erase the cream findings above. Different mixtures and different experiments can produce different answers.
What about people's experiences?
Some people in skincare communities describe more even-looking skin with topical copper peptides. Others report darker-looking patches or irritation. These are anecdotes: personal accounts, without a controlled comparison to show what caused a change.
Both kinds of account can raise a useful question. Neither tells us how likely the same experience is for someone else. An enthusiastic review and a worried review both deserve that limit.
Take a clearer question with you
The GHK-Cu page looks at the human skin research. The comparison explains why Melanotan II belongs in a different discussion. A shared interest in appearance doesn't make the compounds interchangeable.
This page can't identify a patch or interpret a changing mole. Those are personal care questions for a licensed clinician. It can help you ask something more useful than “Will it brighten me?”: what change is being discussed, and did the study actually look for it?