Ahh, he's so cute! If this is the little guy you said you were having troubles with colours looking dull, I think all you need to fix him up, is these 2 things:
1 - Put a layer allll the way under all your colours, set it to Screen, and fill it with a really really dark colour that complements, for example I would probably pick brown, or maybe orange/yellow?
2 - Put a layer on top of all your colours, set it to Overlay, and fill it with a light colour that complements and evens everything out, maybe a yellow or a light red/pink? Play around with it!

I would give that a try and see how you like it. That's how I brought the colours out in mine and made the lighting look nice on it. Let me know how it goes :)

oh gosh, thank you so much! This is all very helpful.
I have a hard time with knowing what to set layers to and what to do with them lol I know that basically playing around with it is the best way to learn, but it's hard to when I don't know where to start. However, I will certainly try this out!
Thank you again .