How to find good material color choices for a Stylized PBR approach?

Hey all, so currently I am trying to wrap my head around how to go about making textures that are a mix of stylized and PBR. The one thing that currently has me stumped, however, is deciding what color combinations should go into my diffuse textures. In realistic texturing, you just have the color of the material, say steel, which is grey-blue-ish, and maybe you have other details on top of that (like grime/discoloration/etc), but that base color doesn’t change from the true color of the material. However, in stylized textures, you really have the freedom, and really the need, to mix all sorts of colors into that diffuse map. For example, in the image below, in just the ‘seemingly’ solid grey/steel looking area of the armor, I can see the colors: green, brown, blue, dark purple, bright purple, dark red, etc.

And that is more subtle color combination than I want to make myself. Ideally, I’d want more vibrant color combinations, like the two images below.


When put together into a full PBR workflow, the effect looks something like this: (image on far left)

My issue is, I don’t really know what the rules are for mixing colors together in that way. I can tell if something looks good, but when something doesn’t look right, I find myself unable to define WHY it doesn’t look right. My question for all of you is, is there a tool, or website, or some resource that I can go look at to see what colors work together for what materials, or types of materials?

Edit 1: I also just realized that, because of the PBR nature of this ‘attempted’ workflow, what I am looking for is not like normal Hand Painted art. In normal hand painted art, alot of the color variation comes from painting in lighting information, both in highlights and shadows. In this stylized PBR workflow, that type of color/lighting information is kept to a minimum in preference for actual material color information… if that makes any sense?

Edit 2: These images are not my own work. Just examples from the internet to help show what I am talking about.

That is an incredible outline for content creation in general - thank you!