6
This might help you out. Download the following image which lists what css codes are used for each element in each of your themes. This is the easiest starting point.
http://207.212.67.81/legends/storage/css_codes.jpg(IMAGE WILL BE DELETED IN ABOUT A MONTH)
Another method I use is to screenshot the existing theme and pull into Photoshop so I can sample colors and then search for those color codes in the theme so I can replace them with what I want.
For those that are curious, I used the webmaster plug-in extension for Firefox/Mozilla to show those codes. Very useful little tool that will show lots of other webpage information and point you towards code optimizations.