Yeah, 500 flushes is not really very many. I live alone and I reckon I flush the loo at least three times a day, which would mean the coating needed reapplying every six months. If you're a family then it's probably heading down towards every three months. If this spray can be re-applied by the end-user and isn't too expensive that's annoying but just about OK I guess. If it needs a technician visit and/or it's an expensive coating then it's not practical. An order of magnitude more flushes between recoatings would definitely be better...

...which is strange, since PTFE is naturally white. I think we've become used to seeing it on silver and grey frying pans.

But that said, what's wrong with a dark-colored toilet?

Merely that a coating that retains total choice in colours is more flexible than one that limits the range of colours possible.

And presumably that's part of the contribution here - a nonstick toilet that doesn't look like the ones you get on planes and trains already.

Also, the current fashion in my country is for white toilets - you go to a bathroom showroom, ~95% of what's on display will be white. A design that doesn't require a change in fashions is simpler than one that needs tastes to change.

It would get really dirty before you realized it. With a white toilet, it's really obvious when it needs to be cleaned.

All colors are wrong. So that you can properly see a clog, the toilet must be clear glass.