The problem here is quite simple, it's a matter on how you're handling shadows. They look grey and washed out.
As shadows get darker they usually gain saturation. There might be some exceptions in cases of ambient lighting (Granted it wouldn't effect the darkest parts, more like the middle tones), like when the blue skies is reflecting off the brown color skin. And the reverse also holds true, as things get lighter the lose saturation.
It would be easier if I showed you in a quick overpaint.
As you can see the hair looks a little bit more solid, and the lighting ob the form of the clothing looks a lot more realistic. That's why you try and separate out saturation like this.
