I'd like to know too
I had a similar experience this year with a new hive located in a new apiary. I noticed brilliant yellow pollen that was left around the entrance and on the frames around the entrance since early spring. This new apiary is located in a place where totally different crops are grown than those at my original spot so I wasn't all that familiar with everything that grows in the area. When driving through the area, nothing that bright yellow was noted and the owners of the property where the new apiary is located didn't have a clue of what the source might be.
I put some frames in with just starter strips for the bees to pull the comb without foundation. When I was back there two weeks ago, this one hive had pulled the new comb in day-glo yellow. It's startling but beautiful!
The really interesting thing is that I have 3 hives in this new location but only this one hive is pulling the comb that is this color. Go figure.
Think like a bee - focus!