Some differentiation seems needed here. It's clear extreme hypersensitivity (hyperseclectivity) to one or more particular colors to the point where they can be unbearable exists among people on the spectrum. This seems quite something else than being very bothered by high contrast, extremely 'loud' or highly reflecting colors. The latter sensations seem very common to anyone and it's likely they would be considerably more intense to people on the spectrum. As for the numbers: the former might affect a number in the order of magnitude of a few percent, while the latter may even involve a majority. Is there more than a rough educated guess?