Hm. If you're using a tablet with a screen it's display settings might be different from your monitors.
If you're struggling with subtle color changes here is a video with a few methods. The first one (manual blending) is probably what you will want to be using as it gives you the most control. I don't think he mentioned it but having the color picker hotkey is crucial.
Overall great work! I like how you started adding volume to you skeleton's torso and head. It helps a lot with the perspective.