Color support for background agent tree display

Feature Request

When background agents are launched, Claude Code renders an inline tree:

⏺ 3 background agents launched (↓ to manage)
   ├─ ♛ Golds — inline banner test
   ├─ » Howlers — howler-alpha
   └─ ✦ Whites — code review

Request: Apply color to each agent line based on the color field in the agent's frontmatter definition (~/.claude/agents/*.md).

Context

Custom agent definitions already support a color field in frontmatter:

---
name: howlers
model: sonnet
color: orange
---

The color field currently only affects the /agents interactive picker UI. When agents are spawned programmatically via the Agent tool (e.g., during multi-agent orchestration), the inline tree display renders all agents in the same default color — no visual differentiation.

What we'd like

When rendering the background agent tree, Claude Code would:

1. Match the agent's description or subagent_type to an agent definition in ~/.claude/agents/
2. Read the color field from that definition's frontmatter
3. Apply that color to the agent's line in the tree display

This would give users immediate visual feedback about which agent types are running — visible from across the room during long multi-agent workflows.

Why it matters

Multi-agent orchestration protocols (like Spectrum Protocol) use 10+ specialized agent types running in parallel. Each has a distinct role (planner, worker, reviewer, tester, debugger, etc.) and a designated color. Without color in the inline display, users can't quickly scan which agents are active — they have to read each description line.

The infrastructure is already there:

• Agent definitions have a color field
• The inline tree already renders agent descriptions with glyphs
• Claude Code's TUI renderer already supports colored text elsewhere

Alternatives explored

• Hooks writing to /dev/tty: Blocked by sandbox
• tmux display-message: tmux not available in sandbox
• CMUX notifications: Work but are popups, not inline
• Status line ANSI colors: Works but is at the bottom, not inline with the conversation
• PreToolUse additionalContext: Doesn't fire for Agent tool, and wouldn't be colored anyway

None of these put colored text inline where the agent tree renders.

Mockup

⏺ 3 background agents launched (↓ to manage)
   ├─ ♛ Golds — inline banner test        (rendered in yellow)
   ├─ » Howlers — howler-alpha             (rendered in orange)
   └─ ✦ Whites — code review              (rendered in purple)

🤖 Generated with Claude Code