I'm certainly not the
artiste' in this family, but the one that is, (
Mrs. C) has always produced vibrant, clear colors in her much appreciated watercolor landscapes (specializing U.S. New England lighthouses). I asked her about your query and she began explaining her techniques for mixing the paints... and then gave me this link:
http://www.fountainstudio.com/watercolor%20tip s/tip-mixing_colors.html . One can see the neccessity of understanding the various sections of colors to mix to achieve the desired results... See if it helps and good luck!