terminal: Make `rgb_for_index` take a `u8` instead of a `&u8` (#8726)

This PR makes the `rgb_for_index` take a `u8` instead of a `&u8`.

`u8` is `Copy` and is only 1 byte, so there really isn't any reason to
pass a reference to it.

Release Notes:

- N/A
12440d5e0dMarshall Bowers committed on 3/2/2024, 9:51:46 PM· committed by GitHubparent4b81b15
1 file changedLine totals unavailable