Feature request: set session color at launch (--session-color flag or sessionColor setting)

Is your feature request related to a problem?

I run several concurrent Claude Code sessions, each dedicated to a lane of work (local test runner, remote test deploys, mobile builds, ticket triage), and I use /color to tell the sessions apart at a glance. Each lane is launched from a shell wrapper (claude --blue, claude --green, ...) that passes a lane-specific slash command as the startup prompt.

The session colour can't be set the same way. /color is interactive-only:

• no CLI flag (--session-color or similar)
• no environment variable
• no settings.json key
• SessionStart hooks can only return context/metadata, they can't execute slash commands
• only one startup prompt can be passed positionally, so you can't chain /color blue with another command

The only workaround I found is macOS System Events keystroke injection from the wrapper (sleep 4, then literally type /color blue⏎ into the window), which needs Accessibility permission and breaks if the window loses focus during launch.

Describe the solution you'd like

Any one of:

1. a --session-color <color> CLI flag
2. a sessionColor settings.json key (usable via --settings)
3. hooks being able to queue slash commands at session start

Option 1 is the simplest and composes with wrapper scripts.

Additional context

Claude Code v2.1.211, macOS (Warp terminal). Colour-per-lane makes multi-session workflows much easier to keep straight; would be great for this to be scriptable.