New function colour: unsafe

That's not just about collections: the whole host of potential bugs could be eliminated if you are under a restrictive colour that prohibits using C/C++/etc. As for the standard collections: some algorithms don't need collections (standard or otherwise) at all, and some can't use standard collections even if they wanted to (e.g. realtime code). For the purposes of the latter we already have @nolocks and @noallocations; perhaps there's some cross between those and "utmost safe".

If to move these discussed colour schemes to their logical conclusions (including other flavours of safety I mentioned above), we may end up having a robust eco system where if you don't have a certain level of colour "clearance" you won't be able deploying the code to certain environments (realtime code for aircraft or a nuclear power station). Normal user apps won't need those (except maybe those using swift in realtime audio code).