Style: candidates list is hard to visually parse

### Problem
Let me first say that I like the cli UI redesign. This has the potential to making it easier to work with.
Unfortunately, I am still having a hard time reviewing the candidates list as it had the following coloring logic:
```
(white) candidate
(yellow) diff
(white) candidate metadata
```
This makes the white lines blend together between neighboring candidates.

Example:


I would suggest to make the metadata (i.e. MusicBrainz, CD, Year, Country, etc.) be gray like we now have with the musicbrainz urls (love that part - kudos)

### Setup

* OS: Arch Linux
* Python version: 3.11.7
* beets version: 1.6.1
* Turning off plugins made problem go away (yes/no): n/a