There are a couple reasons why you might want to consider painting your hex. One is to make it more stealthy. Painted black, it can blend into a background of trees especially in wintry weather when leaves are gone. Another reason is for protection from sunlight.
If you are using a KIO Hexagonal beam, the only components subject to serious sunlight degradation are the fiberglass spreader arms. The fiberglass is UV stabilized for endurance against ultraviolet degradation but still, over time, there will eventually be degradation that might appear as flaking on the surface. How soon this happens depends on the area of the planet you are located. A coat of paint on the spreader arms can greatly lengthen the life of your spreader ams from UV degradation. You can clean/degrease them with a good solvent such as acetone or methyl ethyl ketone…”M.E.K.” (follow their label directions!) Then use a good primer-allowing it to cure at least two days. Finally, finish with a good top coat of flat black, or the color of your choice.
Another approach is to wipe off the dust and use a spray can of Rust-oleum Universal which is a combination of primer and paint. It comes in flat black as well as other colors and a single coat is probably sufficient.
Whatever approach you use for painting, here are a few tips to keep in mind. Do not sand the fiberglass; paint will adhere fine without sanding. Either brushing or spraying is fine. But do not use metallic paint because the conductivity of the spreader arms might interact with the wires and detune the antenna. Do not paint the wires themselves. The paint will change the permittivity of the wire insulation and detune the antenna. Unless you just want to change the appearance, there is no need to paint the baseplate or the center post since they are made mostly of aluminum and stainless steel and will not degrade significantly in weather. That leaves the fiberglass spreader arms.
Painting the spreader arms before installing them on the beam is the easiest approach. You can remove the wire attachment hardware and use small pieces of masking tape to mark the locations where they were on one arm only, in order to cover the arms well. Or you can put masking tape over the wire attachments to keep paint off them. Or you can just paint them too. But making adjustments of their locations later might be harder, of course.