Normale qu'elle soit aussi jaune ?

Get this every now and then with different seed phenos thought it was like a leaf mutation as anyway it never seems to harm the plant in anyway

That's most likely a pigment mutation although very yellow indeed! If you look at my lilac diesel diary she has a pigment mutation herself. I would say nute burn but your not giving her nutes so no way and nute burn usually starts on the outside of the leaves or generalizes in burn marks. Hope this helps.

It's a chlorophyll issue. Get some epsom salts and put a pinch of it in a spray bottle and spray the seedling. Spray her 3 times for a week. Do it at just as lights go out or when the first come on.