vision, so bees can see the three primary colours of UV, blue and green (they
can't see red though!) in the way that humans detect Red, Blue and Green.
when bees go off to collect nectar, they are attracted to colours of flowers
which act as signals for them about the type of flower colours that provide more
or less nectar. they will favour certain colours over others, this means that if
they have found yellow flowers to provide more nectar they're more likely to
visit yellow flowers. there have been many experiements carried out that prove
that bees can see colour and many have trained bees successfully to favour
certain colour over others. you should read about the work carried out by Von
Frisch early 20th century which prove this, and many that followed after that.