Since commit 2811adc0 we get colorized gcc output. Hmm. That's unfortunate for Emacs users (I'm probably one of the very few). Emacs parses the compiler output and now it cannot match the error messages anymore.
Would it be possible to add some variable to disable the coloring? (There's more than just this GCC diagnostics-color.) Something like DONOT_COLOR. This would be in the same category as QUIET, I guess.
But really, I'm curious what people use to develop RIOT-OS. VIM?, Eclipse? Atom? Emacs?