Most oils are dyed "bronze" which we call Amber, because oils are expected (by most of the general public) to look bold and amber.
Redline uses red and orange dyes to differentiate its products, GC and Schaeffer's use blue/green, and of course, Royal Purple uses a specialized red/blue dye combination.
Most additives, right after reaction and processing, are clear. Bronze and/or red dyes are added to differentiate the additives. Sometimes the metals in certain additives, such as MoDTC and calcium and magnesium sulfonates, tend to darken the additive, so the above dyes are added to mask the darkening.
ATF's and most PS fluids are dyed red to detect leaks.
AC compressor fluids are dyed with a fluorescent dye so a blacklight source can be used detect leaks as well.
[ June 15, 2004, 11:29 PM: Message edited by: MolaKule ]