To save everyone a click, cave paint has some sun-blocking properties. There is literally zero evidence that people covered themselves in cave paint to protect from the sun.
Indigenous Australians have been observed using mud to protect themselves, and providing they recognised the need to do so it is much more likely that cave people would have observed pigs and hippos doing this and used readily available mud to shield themselves from the sun rather than routinely covering themselves in difficult-to-make pigments.