[Bug] Ultrathink rainbow animation not visible on iTerm2 light theme

Question

**Bug Description**

Titre suggéré : "Ultrathink rainbow animation not visible on iTerm2 light theme"

Body :
  - iTerm2 with light theme
  - The ultrathink/extended thinking indicator doesn't show rainbow colors (likely contrast issue with light background)
  - Expected: rainbow animation visible like on dark themes

**Environment Info**
- Platform: darwin
- Terminal: iTerm.app
- Version: 2.1.71
- Feedback ID: c315e324-23e8-488b-9e2e-6e9fffd279db

**Errors**
```json
[]
```