At the foundations and often otherwise, the bees mix propolis in with the wax. This makes the wax brown. For most of my uses, I like that just fine since I dip my boxes in beeswax and rosin. But I think the yellow looks very nice. If you want it lighter, make thin sheets and leave them in the sun (in a container of course because the sun will melt them). The sun bleaches them pretty quickly.
