Not really, they've just made it super implicit. Any FFI calls are now implicitly coloured, same with anything CPU-heavy.
Like their approach to type annotations, I think this will be a mistake in hindsight.
That said, you're right in that one may have to make some changes to code to get around some new problems. The problem with FFI/CPU-heavy functions is that they prevent _other_ fibers from being scheduled while they run.
If it becomes possible to implement work-stealing, then that would mitigate the problem. It would also be solvable by sprinkling "yield to scheduler" calls throughout such functions. Annoying and not always possible, but, since in these cases the signature would not change, technically not coloring.
[1]: https://glyph.twistedmatrix.com/2014/02/unyielding.html