Finally, there is a nightly that has these changes! I wanted to try them for weeks now 
While @jntrnr’s screenshot only shows one error with black-on-white text, I wanted to see how this looks with warnings and white-on-black. So, I ran my clippy-diesel branch with RUST_NEW_ERROR_FORMAT=true, which looks like this (PDF).
Quite nice and much better than before, but still noisy. It’d be interesting to see if we could combine some messages about the same line/span. (Also, some spans look wrong, i.e., they only underline one character, but that may be a problem with clippy.)