How do bees choose which flower to visit?

I watched about two dozen bees around a flowering sage bush this afternoon and got to wondering how the decide which bloom to go to. There seemed to be no rhyme or reason. I would see several bees go into the same flower while there were some that did not seem to get any action. They would go in, back out buzz around and dive into another seemingly at random.
Do the blooms give off some kind of pheremone when they are ready for pollenation?
Is it a color thing? They all looked the same to me.
Do they watch each other on the sly and go for the most popular? I know they do some kind of dance at the hive to tell their cohorts where the pollen is.
Any ideas?