Where Does the Wax Come From?

Bees excrete wax from their abdomens.  It comes off in scales.   This is what they use to build comb with. 

New wax is white, so new comb is white.   It gets yellower and darker as the bees track pollen and propolis all over it.   

Old comb gets quite brown because they've used it again and again and have tracked stuff all over it.