I do best when I pull colours from a print, photo or other palette.
I love pinterest for finding different colour combinations.
My son wants a red, black and white quilt. That is easy, I have been collecting prints for a year now. My challenge is deciding on the pattern and cutting up the fabric.
Back in the 1980's I made a Quilt in a Day Trip Around the World quilt. It was peach and green (very 80's colours), one of the greens is too dark. It has bugged me ever since, but not enough to take it apart and change it out, especially 30 years later.
I love primary colours for flannel and denim rag quilts. I do not worry about the colours for them.