Add --color CLI flag for session color

Feature Request

Add a --color CLI flag to set the session prompt bar color at launch, similar to how --name / -n sets the session name.

Motivation

I use multiple Claude Code sessions simultaneously and want to visually distinguish them. Currently:

• --name lets me set a session name from the CLI — great for scripting
• /color only works interactively inside a session — no CLI equivalent

This means I can't fully automate session identity setup via a shell alias/function.

Proposed API

claude --color red -n "my-session"

Available colors would match /color: red, blue, green, yellow, purple, orange, pink, cyan, random.

A random option would be especially useful:

claude --color random -n "my-session"

Use Case

# Shell function that fully auto-identifies each session
claude() {
  command claude --color random -n "$(random-name)" "$@"
}

This pairs naturally with the existing --name flag and would make multi-session workflows much smoother.