New function colour: unsafe

[John_McCall]

@John_McCall

I would like to separate this discussion of "utmost unsafe" from the original conversation about precondition-unsafety. I think it's a much more marginal feature with much higher implementation requirements, and it's basically taken over the thread. Do you folks mind if I split it into a different thread? Would you like to start that thread, @tera, or should I?

I tried several times to split a few posts over to a new thread, but I ultimately decided that the conversations were too interwoven for that to work — I would've had to edit posts, which I'm always reluctant to do, and it would have destroyed a lot of useful context. I've therefore just created a new thread to talk about "utmost safe". Please feel free to continue that line of discussion in that thread.