Most, if not all new high quality speakers today their cones are of polymer construction, very few are paper any longer. As such they are more imune from sun damage IMO. Custom stereo shops use speaker grill cloth to cover speakers with. The cloth is usually black and is not a felt or carpet like material. It is more of a screen like cloth that can be stretched over an MDF frame that the speaker is mounted to. The cloth can also be painted to match your interior color. I had a hard time finding any around my part of the country. I eventually scored some through a friend of mine who knew someone who does custom stereo work at home. I have no idea where he gets it.