Hey man, sorry about my previous comment, didn't want to sound harsh or anything so if it came across like that, my apologies
Must be that you are doing very very smooth transition and keeping your colors really close together which makes it hard to see on a picture with direct lighting!
Skintones are some of the hardest things to get right and it can be hard to get the right amount of contrast in them. What I did was indeed check out the WIP's mentioned above as some of those people have insane skintones in their arsenal...
Good luck man!