I have numerous hardy geraniums in my garden but I find that BBs prefer those that are blue through to near white.  They seem to almost completely ignore the pink through to magenta ones, although they love the dark flower of geranium Pheum.

Does the sight of BBs and bees in general restrict their colour range? 

I had thought that the red field poppy was a favourite but, although I have a couple of huge plants of these, they too are ignored in favour of the paler geraniums.

     

My bees go for pink geraniums but that’s because I don’t have any blue/purple ones.

Bees have a slightly different colour vision that can’t see red but can see ultra violet.
They will go for red flowers sometimes due to them having ultra violet patterns that we can’t see but seem to generally prefer blue/purple or white fowers.

I’m sure there must be a better example somewhere but this is the best I can find at the moment
Bee’s eye view

     

Thank you Kate, that’s very interesting.  I must divide up my “bee preferred” geraniums and spread them around the garden.