Been looking into this for a while and not got any satisfactory answers, however...
1) ANSI escape sequences do work in a terminal on Linux
2) if you can tolerate a limited set of colo(u)rs try this:
print("hello", end=''); print("error", end='', file=sys.stderr); print("goodbye")
In idle "hello" and "goodbye" are in blue and "error" is in red.
Not fantastic, but good enough for now, and easy!