Optional per-environment colors in the thread sidebar

[Oghara]

I regularly switch between local and remote environments in T3C, and it can be hard to tell which environment each thread belongs to.

Would you be open to optional per-environment colors in the thread sidebar?

I built a local desktop prototype to test the idea.

• Choose a color for each environment under Settings / Connections.
• Show it as a narrow marker on each environment's thread rows.
• Leave the existing styling unchanged.
• Store the choice locally on the client, keyed by environment ID.

Here are some screenshots

I found a few related proposals. #6875 tackles the same environment-identification problem with custom machine icons and notes that color alone is less accessible. #6705 suggests a similar color marker for projects, while #7836 explores grouping threads by environment.

I can share the implementation details if useful.