I was wondering this also, as mine are right next to a OSR field . Flying towards it and coming back with yellow pollen, so i thought OSR pollen.But agree others have said different colours and has got me a bit confused.
If you look at a pollen identification chart (IBRA)
it will show OSR pollen as a sort of light olive colour, however, i am lead to believe that this is the colour it would appear under a microscope.
perhaps someone can confirm that?