Bees on broom (Cytisus scoparius)

I noticed a lot of bees entering hives with their backs and pollen loads a bright orange. I'd seen bees with white backs from balsam (Impatiens glandulifera), and even yellow all over from dandelion (Taraxacum officinalis), but this was the first instance that I had seen of orange backs.

Someone drew my attention to a big patch of broom about 1 km from my apiary. I visited it with the camera . . .

With flowers that are not fully open, the bees force their way in below the upper petals.