The front view still has more shadows above his eyes than the other views xP
I don't think you need another colour, instead I think you could work with the existing colours to make them contrast better (lighten up the dark grey or maybe even merge it with the blue of the shoes since it's not really doing any noticeable work, maybe lighten or darken the blue of the shoes since it's very similar to the dark purple of the hair/socks).
It looks like you're struggling with the form of the shoes, it seems inconsistent from sprite to sprite. When in doubt, grab some reference images! Those cartoony shoes look like they could be the same form as half of a pear (with the leg growing up out of the narrow end), so perhaps studying how light affects a pear (or half a pear) would help. You should also study feet/shoes to get a better general understanding, and then exaggerate the shape for your sprite.
As for picking colours, I usually start with the midtone, plop it down, and then pick shadows and highlights by progressively decreasing or increasing the value and shifting the hue towards some common ambient shadow/highlight colour for each colour. I use the HSV sliders instead of the RGB sliders, which make this process much easier, since I can adjust value and hue directly.
When first choosing the midtone, I don't choose it in isolation, I look at my existing colours and consider the general look I want. If I want a "blue" object, that doesn't mean my midtone will actually be blue. If the scene is meant to be warm, my "blue" might be a purplish grey or something. The goal is that it looks blue relative to the rest of the colours. This keeps the colours unified.
