Hi to you in France.
In crested geckos, can you roughly work out what colour babies you would get colour wise. I think depending on their colour, they can have genes for yellow,black, white, red to varying strenghts or amounts.
For instant a bright orange would have a yellow and red gene, a pale orange would have a white gene, red and yellow genes. Crossing two pale oranges together might produce a white ? a red and a yellow, as well as a bright orange and a pale orange and so fourth ?
Two greens who would have a large amount of yellow and black with small amount of red, might produce green, brown, red, blacks, yellows, oranges .
Just an idea anyway

If only it was that easy but at least it is more likely.