The guy we bought the bee hive supplies from
had some good advice about painting bee boxes.
He recommends the big box stores of Lowes and Home Depot because they
usually have a few cans of mixed latex paint that didn't quite turn out to be
the right shade of a color they were going for. These cans are a
fraction of what they usually charge.
Most people paint their boxes white, but he points out how they stand
out from a distance, and a more appropriate color might discourage the
random bee box thief. Luckily we don't have that problem here due to
being tucked so far back in the woods.