`ansi` theme is rendered as explicit RGB colors instead of terminal ANSI palette indices

[tummetott]

What version of Codex CLI is running?

codex-cli 0.105.0

What subscription do you have?

Pro

Which model were you using?

gpt-5.3-codex

What platform is your computer?

Darwin 24.6.0 arm64 arm

What terminal emulator and version are you using (if applicable)?

Wezterm

What issue are you seeing?

Continuation of #1618

When tui.theme = "ansi" is selected, the displayed syntax colors do not follow the terminal’s configured ANSI palette. The current behavior appears to render syntax highlighting with explicit RGB values, which bypasses ANSI index mapping in the terminal.

So in other words: the ansi theme is just another bundled theme that hardcodes random colors instead of using the ANSI-indexed terminal-palette

Relevant code paths suggest this behavior is intentional in current implementation:

codex-rs/tui/src/render/highlight.rs:125: maps ansi to EmbeddedThemeName::Ansi
codex-rs/tui/src/render/highlight.rs:380: applies syntax fg as RtColor::Rgb(fg.r, fg.g, fg.b)
codex-rs/tui/src/render/highlight.rs:371: comments that syntax themes produce RGB colors

What steps can reproduce the bug?

1. Configure a terminal with clearly customized ANSI palette colors.
2. Set Codex config to:

[tui]
theme = "ansi"

3. Open Codex TUI and view syntax-highlighted code content.
4. Compare token colors against terminal ANSI palette slots.

What is the expected behavior?

When using the ansi theme, codex should actually use the terminals ansi palette and don't hardcode some random RGB color for syntax highlighting

Additional information

No response

[tummetott]

Same story applies to base16 and base16-256. They simply do not pick up the terminal colors

[thesofakillers]

can confirm. result of this is that e.g. the diff colors are off. e.g. here's codex's gruvbox light inside a iterm2 gruvbox-light colored terminal, using some off-theme pink and blue rather gruvbox's red and green.

the pink and blue seems to apply for all color themes to varying extents

[tummetott]

can confirm. result of this is that e.g. the diff colors are off. e.g. here's codex's gruvbox light inside a iterm2 gruvbox-light colored terminal, using some off-theme pink and blue rather gruvbox's red and green.

actually this is more related to #12912

diff background colors are currently hardcoded.

On a sidenote, all built in themes except ansi, base16, and base16-256 are supposed to use bundled RGB values. They are not meant to inherit or load colors from the terminal emulator. The three exceptions mentioned above should theoretically use the terminal’s ANSI colors, just mapped to different ANSI indexes. But that’s currently not the case.