Terminal Color

Color in this tool is decoration painted on at the last moment. Every signal it carries is also carried by a word, a symbol, or a prefix character that is present whether or not color is on — so a reader who cannot distinguish two of these hues, a reader on a monochrome terminal, and a grep in a pipeline all see the same information.

Whether color is emitted at all is decided by --color, NO_COLOR, TERM=dumb, CLICOLOR_FORCE, FORCE_COLOR, and an isatty check on the destination stream (NO_COLOR/TERM=dumb win over CLICOLOR_FORCE/ FORCE_COLOR when both are present); see --color in the global options. This page is about which colors may be emitted once that decision says yes.

The approved palette

Every ANSI escape this tool writes comes from Painter in packages/core/cli/src/color.rs. It is the only place in the codebase that emits an SGR sequence, and it emits exactly these six:

SGR code	ANSI name	Emitted by	Used for
31	red	Painter::red	the Error prefix on a failed run; the error severity word in a lint report; removed (-) lines in a diff
33	yellow	Painter::yellow	the warning severity word in a lint report
32	green	Painter::green	added (+) lines in a diff
36	cyan	Painter::cyan	the try prefix on a repair suggestion; @@ hunk headers in a diff
1	bold	Painter::bold	---/+++ file headers in a diff
2	dim	Painter::dim	de-emphasized decoration; defined but with no call site today

Painter::wrap closes every one of them with the reset 0, so no escape outlives the string it was applied to.

Color is never the only signal

Any new severity, status, or category color must pair with a mandatory text label — a word, a symbol, or a prefix character that is printed regardless of whether color is enabled. Adding a hue that is the sole carrier of a distinction is not permitted, no matter how well-chosen the hue is.

This is what makes the red/green pair above safe despite red–green being the most common form of color vision deficiency. The two never distinguish anything on their own:

• Severity uses red and yellow, and colors the severity word itself — the text reads error or warning either way. A lint report row is tab-separated and machine-readable before it is colored.
• Diffs use red and green, but the underlying text is a unified diff: every line already begins with a literal -, +, or space, and the coloring is applied to the finished diff rather than folded into its generation.
• Failures color a prefix that spells Error, and repairs one that spells try.

Remove all six codes and no output becomes ambiguous. That property is the requirement; the specific hues are not.

Why the base eight, and not 256-color or truecolor

The codes above are the original eight-color SGR set, which a terminal resolves against the user's own theme. A reader who runs a palette chosen for their vision — or simply one with better contrast than the default — gets that remapping applied to this tool for free. Emitting 38;5;<n> or 38;2;<r>;<g>;<b> would pin an exact RGB value and override the one adaptation the reader has already made for themselves.

So extended-color escapes are excluded on purpose, not for lack of need. Bold and dim are attributes rather than colors and remain available for emphasis that must not depend on hue at all.

Enforcement

tests/cli/color_palette_contract.rs reads color.rs as text and asserts that the set of SGR codes it emits is exactly the six above. A seventh code — including any 256-color or truecolor escape — fails the test until it is added to this table, which is the point at which the pairing rule above has to be answered for it.

The same test checks that this page still lists every code and the function that emits it, so the table cannot drift from the source.

HTML report color

--output html is a separate rendering surface from the terminal: it is CSS, not SGR escapes, and it is styled by the HTML_STYLE constant in packages/core/cli/src/report/interop.rs. It is a small, fixed palette in its own right:

Hex	CSS class	Used for
#D55E00	.gate.fail	the gate line when flat.gate_passed is false
#0072B2	.gate.pass	the gate line when flat.gate_passed is true

The same rule as the terminal palette applies here: color is never the only signal. The gate line always prints the literal word passed or failed next to the colored text, so the distinction survives grayscale printing, prefers-contrast, or a reader who cannot separate the two hues.

These two hex values are not the terminal palette's red/green — they are drawn from the Okabe-Ito colorblind-safe palette (vermillion and blue) instead, because unlike the ANSI codes above, a browser renders a CSS hex value exactly as pinned, with no user theme remapping it. Red/green is the pair that is hardest to tell apart under deuteranopia/protanopia, so this surface avoids it where the terminal palette does not need to.

tests/cli/html_report_palette_contract.rs reads interop.rs as text and asserts that HTML_STYLE uses exactly these two hex values for .gate.fail and .gate.pass, and that this page documents both.