Thanks for the replies.
Using version 10.5. I did start doing just that, adding my own colors, but then I accidentally changed some of the default colors by accident and can't figure out how to get them back because I don't know what the mixture of colors was. I'd like to create my own palette based upon the default and several others but leave the originals alone in case I screw up again.
Pressing the color spec button allows you to modify the existing palettes but I don't see anything there that creates a new custom palette from scratch.