You get the color picker if the "schema" behind the particular property editor says "x.y.z.color is a type: color property".
So it won't show up for arbitrary custom properties, no matter what you name them, but it should show up for all first party properties where you enter a color. That's the bug that I was alluding to in my earlier post.
Since it sounds like you're asking for the ability to define a custom schema for arbitrary properties, which would be a new feature, you're actually asking for something that we're already tracking internally; see: