I mean what makes plants or plant life offensive to people? I just don't get it.
One word: tentacles. Obviously most realistic plants wouldn't need a warning, but hentai anime monster plants might.
CG Bytes is essentially a spin-off of Renderotica. I think it's supposed to be "R" rated instead of X, but since Renderotica is itself _way_ beyond what most people expect of porn (sorry, but no, it's not necessarily what people would expect), including lots of bloody cutting and burning torture, CG Bytes is, IMHO, more X than R. And it has a whole lot of tentacle products.
Well, for that matter, the same could be said of putting the text in red if the person who has the visual impairment is color blind.
Animated text will actually be difficult to read for many, impossible to read for some reading disabilities, and even possibly seizure triggering for some. Where a color blind person just wouldn't get the red cue and would have to get the cue from something else. Which you've said would be its boldness.
Frankly, a better solution would be to just make an adult section, clearly label it in English, maybe write out something like "WARNING: Must be 18 or older to access this adult content." Bright bold red stuff is randomly distributed on the page is distracting and draws attention rather than prompts avoidance.
It would be nice if it were possible to separate out sexy clothes vs. practical ones, but I don't think the community has ever made enough practical clothes to make the differentiation work. Personally, I think the easiest standard is what the media use: if it would be OK on a magazine cover in the supermarket or on TV, then it's OK.