What's the evidence that the colors were added later?

[Rafal]

I don't know if it was discussed before.

It is often said on this website that the painter had no clue what he was doing and was using totally random colors.

But for me the case of Gemini shows that sometimes he knew what he was doing:







There is apparently some line of tradition that in Gemini man is green and woman is blue and he follows this tradition.

So either he knew it or he was looking at the original inspiration just like the man who drawn the lines. Or he was the same man.