fix(color): change parse error message to single color

[EdJoPaTo]

Found while enabling https://rust-lang.github.io/rust-clippy/master/index.html#assertions_on_result_states

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.2%. Comparing base (cf67ed9) to head (10f52c3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1139 +/- ## ===================================== Coverage 94.2% 94.2% ===================================== Files 60 60 Lines 14630 14632 +2 ===================================== + Hits 13790 13792 +2 Misses 840 840 ```

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[EdJoPaTo]

These messages should be lowercase.

Thought about that too, but it's about the struct Color.

[joshka]

These messages should be lowercase.

Thought about that too, but it's about the struct Color.

Failed -> failed

[EdJoPaTo]

My main intention was to enable this lint and fix the mistake of outputting colors instead of color. As this seems to be more complicated about stuff I don't use in the first place (= don't care much about it) I'll just close this.