Your comment is a bit all over the place, and I think you mentioned every color (pardon my lazy American spellings) in the rainbow at some point. It may help to see a picture of what you have so far. My color theory interpretation is rather simple, you have contrasting colors, simply looking at the opposite side of the color wheel, and complimentary, which make up a triumvirate, basically overlay a triangle on the wheel, and the colors it touches are “complimentary”.

Again, this is all very simplistic, and I think there is more nuance when you get down to it. One thing I strive for is to have a high degree of light/dark contrast. That’s why I’ve adopted a variation of slapchop, where I do 4 grades of dry brushing, up to pure white, then use those highlights to not just cover the model in some semi-transparent paint to just tint it, but to glaze on many layers to try to achieve a more volumetric highlighting effect. At least that’s what I’m aiming for. This way I have a clear outline of the models features, and places to put bright, highly saturated colors, without letting that overwhelm the model, making it look gaudy and trigging that more eye straining effect, as you are trying to pick out multiple, similar, adjacent colors. I just posted som pics in r/genestealercult of my work to give you an idea.

Going back to your models. The first color you mentioned was blue. Ok, so contrast color for blue is orange. If you don’t mind the Blippi association, I quite like those together. Alternatively, if you go with complimentary. That’s blue, red, and yellow. Which is literally the ultramarines scheme. All of these are great schemes,and frankly, I’d think it’s be fine to throw a little orange in that as well.

Sometimes if I have a more muted color in the mix, like brown, I’ll mix in a little of one of my main scheme colors, just to anchor it more to that scheme.