Auto merge of #2283 - RalfJung:color, r=RalfJung
Auto merge of #2283 - RalfJung:color, r=RalfJung

revert --color=always changes

They [cause problems](https://github.com/rust-lang/miri/issues/2277) and they completely break rendering on the playground:
```
   Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 0.47s
     Running `/playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/cargo-miri target/miri/x86_64-unknown-linux-gnu/debug/playground`
[0m[1m[38;5;9merror[E0277][0m[0m[1m: `*mut std::sync::atomic::AtomicUsize` cannot be sent between threads safely[0m
[0m   [0m[0m[1m[38;5;12m--> [0m[0msrc/main.rs:17:18[0m
[0m    [0m[0m[1m[38;5;12m|[0m
[0m[1m[38;5;12m17[0m[0m  [0m[0m[1m[38;5;12m|[0m[0m   [0m[0m        let j1 = spawn(move || {[0m
[0m    [0m[0m[1m[38;5;12m| [0m[0m [0m[0m[1m[38;5;12m__________________[0m[0m[1m[38;5;9m^^^^^[0m[0m[1m[38;5;12m_-[0m
[0m    [0m[0m[1m[38;5;12m| [0m[0m[1m[38;5;12m|[0m[0m                  [0m[0m[1m[38;5;9m|[0m
[0m    [0m[0m[1m[38;5;12m| [0m[0m[1m[38;5;12m|[0m[0m                  [0m[0m[1m[38;5;9m`*mut std::sync::atomic::AtomicUsize` cannot be sent between threads safely[0m
[0m[1m[38;5;12m18[0m[0m  [0m[0m[1m[38;5;12m|[0m[0m [0m[0m[1m[38;5;12m|[0m[0m [0m[0m            *(c.0 as *mut usize) = 32;[0m
[0m[1m[38;5;12m19[0m[0m  [0m[0m[1m[38;5;12m|[0m[0m [0m[0m[1m[38;5;12m|[0m[0m [0m[0m        });[0m
[0m    [0m[0m[1m[38;5;12m| [0m[0m[1m[38;5;12m|_________-[0m[0m [0m[0m[1m[38;5;12mwithin this `[closure@src/main.rs:17:24: 19:10]`[0m
[0m    [0m[0m[1m[38;5;12m|[0m
```

Sorry `@saethlin,` I think we need to go back to start here and consider another solution.

Fixes https://github.com/rust-lang/miri/issues/2277

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri