Colour theory help

[rose mesa]

Im painting an ultramarine scheme with cold colours, blue highlighted with an icy blue, turquoise grey on black but i cannot for the life of me figure out a way to make a cold red

[stark canopy]

Color theory is very much theory. But that said, you want to travel along the color wheel toward cooler colors. So this would basically be red -> magenta -> purple -> blue. So you probably want your red cool shadows to be a result of mixing your red with a purple or even a blue. If you need to pull it darker, you can use a darker purple or darker blue or add a tiny tiny bit of black.