Ive yet to find a hard and fast rule on clothing. I buy a majority of used stuff from ebay in all colours. Sometimes dark stuff stains and sometimes they dont. Ive got black t shirts that are safe but a pink dress that stained. A dark burgundy dress which is safe yet a red bikini stained after only 10 mins.
I agree that more expensive items seem to be safer and nude tights always help. I tend to just buy what i like and keep checking it when they first wear it.
Skye could wear this outfit forever safely and its nearly all black