impurification

almost all impurities are suitable, not limited to colored impurities.
activated charcoal / carbon can ADSORB (nor absorb) molecules on its surface, probably non-selectively. but the amount of impurities is much smaller than the sample; so impurities can be removed quantitatively with little sample loss.

which syllabus are you talking about?
anyway, it's commonly used in removing colored impurities and is simple. let's remember it.