Remove purple coloring from DocumentBar

[richtabor]

As an affordance, the purple color applied in the DocumentBar is not helping to communicate the "global" nature of templates, synced patterns, and template parts. It's just not connective in this presentation, and with the addition of post type labels in #65167 — arguably, not necessary.

I propose we simplify a bit, removing the purple color within the DocumentBar.

Current

Proposed

[creativecoder]

Looking at this, I see we use color: var(--wp-block-synced-color); in a number of other places, too, here are some that I found:

List View Template Parts

Template Part Block Toolbar

Template Part Block Info

Template Title

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I think this should be consistent, e.g. if the color isn't used for template text in the DocumentBar, then don't use it in the Template info (sidebar) either.

Same for the icon, (unless it's removed from the DocumentBar, see #65167)

[richtabor]

I think this should be consistent, e.g. if the color isn't used for template text in the DocumentBar, then don't use it in the Template info (sidebar) either.

This yes, but the template part block icon is block-level, so I think it's fine to leave it purple in canvas—for now at least.