Quick tip here. Say I want my letterhead to match a particular orange. (just as an example ;-)
All of us on the Mac know what the color picker looks like.
Most of us have done one of two things. Either limit our choices by picking the box of crayons or select the color wheel and then spend 30 minutes trying to "eyeball" and adjust the color to match.
There is an easier way.
Simply select the magnifying glass next to the color bar. Your cursor changes to a magnifying glass. Now just move it over the color you want to match and click. Now you have an exact match!
Once I discovered this tip, I can't tell you how often I have used it.... and my guess is you will too.