The value of "Red" "Green" and "Blue" need to be the same letter/number in order to shorthand.
#ffffff is the same as #fff
#336699 is the same as #369 ("Red" = 33 = 3, "Green" = 66 = 6, "Blue" = 99 = 9)
#c0c0c0 can not be shortened, because the value of "Red" (or "Green" or "Blue" for that matter) is c0, and cant be expressed any other way.
Likeway, #c0ffff can not be shortened to #c0ff, because HTML needs either a 3-digit or 6-digit hex code for colors.
It's not a "rule" per se that #ffffff must be written #fff, its just a lot faster and easier to shorthand what you can. I won't mention file weight, because shorthand hex colors won't save you that much space...
Sorry to resurrect an old thread (truth is, I've been busy with school and had to put this project on hold), but I'm having another problem with my fake tabs.
Basically, I want to make the tabs (and the iFrame they're attached to) have a liquid design: whenever you resize the page, everything will grow/shrink along with it, and they'll stay together.
I'm pretty sure I need to use "width=%" and "height="%" (and probably "position: absolute", or some other positioning code) -- and it might even work better if I use images instead of text (since images can be resized with %) -- but I can't quite make it work. =\