Hey thanks man! Im not too great with my colour theory either but ill share a few things ive picked up whilst ive been working at my painting skills.
I started off being terrified of ruining my drawings with colour so i started surfing around a lot of illustration and fine art sites to get some tips. One thing that really helped me out was just seeing how many different approaches there are to colour and how theres not really a write answer for choosing colours.
Ive kinda left realistic colours behind recently so its generally just trial and error for me. There are a few basic rules though that are meant to help you choose the right colours.
First of all, tone is REALLY important, if you have the right tone in the image then the colours will generally sit well together no matter what they are.
If you want a specific colour scheme then its a good idea to split the colour wheel into thirds and work from only one third. I usually wait until almost the end of the painting and then use a few complimentary colours to mix things up.
Also remember the rule of warm light / cold shadow, or cold light/ warm shadow
Complimentary colours are commonly used to help highlight things in the image, but i tend to use a lot of these nowerdays just to throw extra elements in.
The best tip I gave myself a few weeks back...
Consider these rules but dont live by them. The best thing ive done is take a graphicalal approach and remember that my goal is to paint something thats none photographic. Whats the point of painting something that looks like a photo? I have a camera.