A colour wheel will help, but I find the most useful techniques are either using a colour picker to isolate tones from photographs (great for skin colours) or work in HSB instead of RGB and learn to recognise colours by their angle (0 - 360 degrees). I also use makeup websites, which often have RGB values for a range of human skin tones so people can identify the proper foundation.
Miniatures can be a cool way to work physically because the paint pots are labelled
I'm guessing that's why you suggested it?