At present, test output is done without colour¹ unless RUST_TEST_TASKS is 1. On supported operating systems, colour should always be done, regardless of the value of RUST_TEST_TASKS.

On a normal OS, you're just writing the likes of testing foo... ^[[4mok^[[0m\n, so I don't see what can go wrong with the formatting, assuming it's being done as one write call.

Windows might have race conditions here on account of its make-an-API-call approach; I don't know. (Is it even supported for colouring?) But that's no reason to hold back the Dazzling Glory of Useful Colours from the proletariat ².

_{¹ "color", for those of you who speak en_US.}

_{² Something tells me the proletariat wouldn't be running Rust tests. Too bad. That's his fault, not mine.}