All 89 bee plants
Meadowsweet pollen
Filipendula ulmaria
Greenish cream, in the cream / white range.
FloweringJune to August
PollenFair
NectarNone
SeasonSummer
WhereWaterside, Waste and verge
Damp meadows and ditches. Pollen only, but freely worked.

Easy to mistake for these
Closest pollen colours in our set, measured the same way the pollen identifier scores a match. Colour alone will not settle it, so check the flowering months and what is actually growing near your hives.
Out at about the same time
Saw a load like this going in?
Sample the colour against all 89 plants, then keep a forage record per hive.