Trial and Error are the best teachers! I haven't a clue when it comes to colors. I draw inspiration from laying out fabrics I have on hand keeping in mind the quilt pattern chosen, matching blenders to a printed fabric piece, and viewing what others have done with a block or quilt. I like to google quilts in a certain color ways to see what I can learn from others.
I think this is "Make visual dicisions visually". Quoted from Ruth McDowell