The check only looked at COLORTERM, but tcell also draws 24-bit color for terminals whose description has it (xterm-ghostty, xterm-kitty), so in Ghostty on macOS without COLORTERM the background was never used. Use tcell's rules, and always log which background is used and why. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019reK4DUGYqDUjniWYJvwUW