You’ve seen black ones, white ones, grey ones… Maybe you’ve even seen a pink one or a blue one. Antennas come in all colors and the thing you need to know is, it doesn’t matter.
Signals from distant broadcasts, whether they are over-the-air TV, Wi-Fi, cellular, or something else, don’t care what color the antennas. Most antennas are either bare metal or covered with a plastic shell. Either way, they are engineered so that the maximum possible signal gets to the actual antenna part.
I’m sure you’ve heard somewhere along the way that radio waves and visible light are just different parts of the same thing. This is true, and what it means in this case is that some things that you can’t see through with visible light are almost transparent to radio waves. On the other hand, some things that may look identical to you could look completely different to radio transmissions. It has to do with the actual composition of the material. For example, a black plastic shell that is colored with red, yellow, and blue dyes could be completely transparent, but if the same color is achieved with flakes of metal (as some yellow dyes are) then it will reflect radio waves.
That’s why you shouldn’t paint an antenna yourself. There’s no way for you to know what the composition of the paint is. On the other hand, manufacturers have all that information in front of them and they know how to combine colors in order to come up with what they want without stopping those all important transmissions from coming through.