project panel: Reintroduce project panel knockout color (#21926)

Reintroduces #20760 after it was reverted in #21807

Closes #20572

/cc @danilo-leal 

Release Notes:

- N/A

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Co-authored-by: Cole <cole@zed.dev>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>