Bring back rainbow highlighting for "ultrathink" keyword (as cosmetic feature)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The "ultrathink" keyword used to trigger rainbow text highlighting in the prompt, providing satisfying visual feedback when requesting extended thinking. With thinking now being max by default on Opus 4.5, the keyword functionally does nothing—but the rainbow highlighting was removed entirely.

This feels like removing the ritual without considering its emotional value. I even made a physical "ultrathink" sticker for my laptop. The keyword detection still exists (per release notes about fixing highlighting), but the visual delight is gone.

It's like removing the turbo button from a car dashboard because the engine is always in turbo mode—functionally correct, but you've taken away the intention and the dopamine hit of explicitly requesting deep thinking.

Proposed Solution

Option A (preferred): Keep rainbow highlighting for "ultrathink" as a purely cosmetic feature. When the user types "ultrathink", show the rainbow text highlight even though it doesn't change functionality (since thinking is already max).

Option B (inverse approach): Since thinking budget is now max by default, flip the logic:

• Default = max thinking (current behavior)
• - "think" / "think harder" / "ultrathink" = cosmetic acknowledgment with rainbow
• - - New keywords like "quick" or "fast" = reduced thinking budget for simple tasks

This preserves the ritual while giving users a way to reduce thinking when they don't need it, rather than increase what's already maxed out.

Alternative Solutions

No workaround exists - the visual delight is simply gone. I still type "ultrathink" out of habit, but now it just sits there in plain text.

Priority

Low - Nice to have

Feature Category

Interactive mode (TUI)

Use Case Example

1. I'm about to ask Claude to help me architect a complex feature
2. 2. I type "ultrathink" at the end of my prompt to signal "this one matters, please think deeply"
3. 3. I see the rainbow text highlighting appear, confirming my intention was registered
4. 4. I feel a small hit of satisfaction knowing I've explicitly invoked deep thinking mode
5. 5. Even though thinking is already max by default, the ritual and visual feedback matter for the user experience

Additional Context

I made a physical "ultrathink" sticker for my laptop. The feature meant something to me beyond its functionality. Small delights like rainbow text make tools feel personal and fun. Please consider bringing back the visual feedback even if the underlying behavior is unchanged.