Propolis is very sticky. Your dh could scrape it off the hives into a canning jar when he is working the hives, if you want pure propolis for skin products.
Is it possible that this is beeswax from the brood frames and not the honey frames? The wax on brood frames get darker faster than the wax on honey frames.
When bees emerge from their cells, they leave behind frass. Even though the housekeeping/nursery bees clean out each cell so the queen can use it for a new egg, not all the frass is removed; and this builds up over time.
Along with propolis there will be bits of pollen, and possibly bee parts in the wax. And as wax ages, it does naturally get darker, just from the many bees walking and living on it.
I save the darker beeswax for us to use. It is great for small blocks of wax for the sewing/quilting box, rubbing against sticking drawers and for making emergency candles.
Just an aside...... my beek mentor changes out the beeswax on all the frames in his hives every 3 years. He said this help prevented disease build up in the hive. It would certainly limit the amount of really dark beeswax being harvested.
ETA: Yes, working with temperatures that are too high will burn the wax and it will show in the end product. So far, I have not found a way to completely clean the wax after it has been exposed to temps too high.
