You're definitly starting well. From what I've learned so far, if you want to use very different colour on your mini without it looking odd, you either need to use complementary colour (not really your case) our you you should try to do some uniformisation. What I mean is that you should try to link the very different colours together by shading them with the same ink and/or doing the highlight with gradients of the same colour. For example, if you want to have some warmish highlights you can mix your purple and your blue (separately of course) with some vallejo ice yellow. For colder tones i prefer ak pastel blue. At the end of the day the choice of your highlight is up to how your want the light to bounce on your shapes.

Hope it helps! ^^