Well, you have to understand the hexadecimal number system and basic
color principles. Each color specifier is three two-digit hexadecimal
numbers. They represent, in order, the intensity of red, green, and
blue light in the color. FF is full intensity, and 00 is none. For
example, #000000 is black, #FFFFFF is white, and #FF0000 is pure red.
#808080 is gray and #808000 is a half-intensity yellow. The
ability to pick the primary colors out of a mix comes with practice.
BTW, never use #FFFFFF as a text color in a Netscape document. There is a
bug in the windows version that will make the text invisible. You should
use #FEFEFE instead.