At first, the answer would seem sort of obvious. Just look at the dish in the picture. It’s clearly been painted. Everyone’s seen those big white satellite dishes, they’ve clearly been painted.
The question, though, is not “can a satellite dish be painted” but “can you, the average person, paint a satellite dish.” The answer is…Yes you can do it, although maybe you shouldn’t. If you are going to paint the dish, you should use a matte (non-glossy) paint. That may not make sense to you because the signals are supposed to reflect, but matte paint is better because it avoids stray reflections that can degrade the signal.
You should use a paint designed to stick to metal without additional priming, but avoid a “metallic” or metal flake paint because again, that can cause problems with the reflector doing its job. Of course you should always mask off the inner surface of the LNB (usually that means the white plastic part) to make sure no paint gets on it.
Spray paint would seem to have an advantage over a paintbrush because you need as smooth a surface as possible. The color of the paint doesn’t seem to make a difference because the frequencies you’re reflecting are far outside the visible range anyway.
That’s really the thing. Without fancy instruments you don’t know if the paint you’re putting on will really do a good job reflecting the 15-20GHz signal that you get from satellites, and unless you’re the kind of person who paints cars for a living, how do you know that your technique will be good enough?
If you’re willing to try it, though, post your success or failure stories here along with pictures!