I often get support questions like “I want to change the color of element “X” from default black to red” (or similar). If you have a look into the CSS files you normally should find out pretty fast which areas you need to edit to change colors, fonts and even sizes of specific elements. But sometimes it´s not so obvious and searching for the right CSS selector can be a pain. The famous Firefox addon “Firebug” makes it easy as 1,2 3 to find the right CSS.
Find out more about Firebug at its offcial Website.