Hi,
I can't really add anything other that that I agree that getting a feeling for colour comes from experimenting, ressource material and theory. And use what you have learned to make more 'educated guesses' when it comes to mixing and choosing paint.
I honestly think your miniatures show that you have both skill and sense for colour. So you might be a bit too hard on yourself (I know that feeling when you are unsatisfied...)
Take Bad Juju for example. The colours are fine. Red and green is a very high contrast (probably a slightly more hue into the magenta range would have reduced contrast) but I don't think that this is a problem. What I would do if it was my miniature would be to add more contrast into the greens, i.e. make deeper shadows. If you take a look from a bit afar, the voodoo doll attached to his front sticks out alot (nice brown by the way) which is because it is very sculptural (I hope I'm using the right term here, in German it's 'plastisch'). The moss on the other hand almost apears fla tin contrast. Here you could try to darken it a bit (especially were the light wouldn'thit from above) by using a darker green. If you want to experiment, mix green with purple, or even use a purple glaze, it should be more vivid than adding brown or black to your green.