Headers, primary, and secondary text

• Headers: Use bold. For markdown with various header levels, leave in the # signs.
• Primary text: Default.
• Secondary text: Use dim.

Foreground colors

• Default: Most of the time, just use the default foreground color. reset can help get it back.
• User input tips, selection, and status indicators: Use ANSI cyan.
• Success and additions: Use ANSI green.
• Errors, failures and deletions: Use ANSI red.
• Codex: Use ANSI magenta.

Avoid

• Avoid custom colors because there's no guarantee that they'll contrast well or look good in various terminal color themes. (shimmer.rs is an exception that works well because we take the default colors and just adjust their levels.)
• Avoid ANSI black & white as foreground colors because the default terminal theme color will do a better job. (Use reset if you need to in order to get those.) The exception is if you need contrast rendering over a manually colored background.
• Avoid ANSI blue and yellow because for now the style guide doesn't use them. Prefer a foreground color mentioned above.

(There are some rules to try to catch this in clippy.toml.)