I’m agree with CybrGfx’s advices as usual
-I just want to add my opinion because your work has the same problem than in this thread by VISEone, you need to consider the whole shape as if it was simplified. Once the simplified lighting is done (fig.2) you can start to increase progressively details like in the third and fourth figure.
(First figure is what you have done for now, the same use of the same gradient for everything)

-About color samples you have used…well, i think it limits yourself in the choice of color than anything else.
I have made a video paint over of your work, you can see here (800x600 - time x2 - 16min29 - 46,9MB):
BUT, be careful if you decide to view it, it is 33 minutes in real time and it is a lot more detailed on the head than an usual paint over. I mean viewing it will probably kill your motivation as it can give a precise idea of a finished work.
Now I used a really sharp brush painting on the whole character and the brush left many artifacts in a first time to show you it is not a problem for this kind of character (no perfect baby skin).
I have made this video also to show you I will never limit my colors with something established at the start. You can see also the heavy use of color picker…
At 16 minutes I have tried the use of a screen composite layer to show you a quick undead color~ just for the fun.
I wish this little “tutorial” will help you…