I attended a lecture/workshop today with Sally Collins - a master of precision piecing. She spent some time explaining how she selects color. She picks a main fabric that has good color combinations in it. She doesn't use this fabric in her quilt but takes color from it.
From this piece she will select the basic colors - say 4 or 5. It is the combination of the colors that appeals to her.
And then selects a background which may be one of the colors. Then she arranges a group of values of each of the colors with fabric. Each color may have 5 or 6 values that she will use. Then she mixes them all up and resorts in light, medium and dark and then begin to cut and piece.
She does a mock up of the block first to see if she has arranged to her satisfaction.