Brian, excellent explanation. It does make perfect sense too.
The plants that the bees on my property are currently foraging on are (bees like to forage within 200 feet of their hive, trivia):
I am listing these from the closest to the apiary to the front of my house, where they are happy to go too:
Phacelia Tanacetifolia (but this pollen is purple, like the Fireweed pollen)
Borage
Bachelor's Buttons
Sunflowers
Anise Hyssop, Blue Fortune
Anise Hyssop, Anisata
Great Blue Lobelia
Impatiens Capensis
Mignonette (and man are they mad about this flower!!!!) (and it has the most beautiful perfume I have ever smelled)
Blue and pink fall Asters
Now up to my flower gardens in the yard
Nicotianna
Blue Salvia (Victoria species)
Heliotrope, Marine
Other flowers abound in my gardens, but these listed are the ones the bees are highly attracted to.
When I was observing the bees on the Nicotianna, the pollen in the baskets were white, but like Brian said, a myriad of plants produce white pollen. The flowers are still going strong and beautiful. We have had the perfect weather this summer for flowers, lots of rain, enough sunshine and not too hot of weather. Still, I think that vegetables and flowers have been set back by about 2 weeks by the cool summer weather.
A problem has occurred with the Canna lilies that grow amongst my banana grove. They did not even produce any flowers this year. Normally they have a beautiful red flower that arises far above the foliage. I have always grown these and this is the first year they have never set a flower bud. It has been a strange year for us all, everywhere. Have a wonderful day, beautiful life we live in. Cindi