Honeybees and many other insects have well developed colour vision. Many,
including honeybees even have a three-colour system, not unlike our own
(blue,green,red) except for them it's (UV, blue, yellow-green roughly
speaking). Mark Winston's book Honey Bee Biology talks about this a
bit, but the field is quite complex and has changed a lot in the last
decade or more. Karl von Frisch's book Dance-Language and Orientation in
Honey Bees has a detailed general discussion of work up to the time of
that book's being published in the original German. General textbooks
in Insect Physiology all discuss insect colour vision.
 
Some flowers do have UV coloured parts that act as nectar guides. We
can't see them, of course, but training experiments have shown that
bees can. Not all flowers are so equipped, and some that are may have
bull's eye patterns to radiating spokes, to spots, and other forms.
You can look at flowers with your own eyes to get an idea of the
general diversity of nectar guides, their forms, and so on. When UV
is added to the repertoire of what we can see, the diversity of colours
in the bees' environment goes up. Of course bees see the same nectar
guides as do we in parts of the visual spectra which overlap. Bees
are insensitive to red light, so red marks on flowers would be seen
as black (colourless) by bees.
 
The issue of bees' navigation by UV is perhaps a bit overstated. UV
light becomes polarized as it passes through the atmosphere coming from
the sun. It also becomes somewhat difused. Bees use the polarization of
light for navigation, but all light visible to bees becomes polarized.
I am not sure if UV is special for navigation, or if it is just visible
(to bees) light in general. Perhaps some-one else can comment on that.