Is it ok if part or all the gum graft (tooth) goes white?

Maybe: It is fairly common for a graft to differ in appearance from the adjacent tissue. If you can get back to the original surgeon for evaluation, that's the best way to be sure. Failing that, go to another dentist to have it examined. I have seen several that appear fairly white many years later

Skin sloughing: After the graft, the epithelial layer of the graft would slough off and has the white appearance. As the graft heal, the neovascularization process begins, as blood vessel migrates into the area, forming new capillary network, and the area starts to have a red color showing through. If the graft becomes greenish or bluish, the graft probably fails. Check with your dentist/surgeon.