TerminalTheme

TerminalTheme

Print the current terminal theme (foreground and background colors)

Module type	terminaltheme
Default order	32 (only used by --gen-config)
Module source	src/modules/terminaltheme/terminaltheme.c
Detection source	src/detection/terminaltheme/

Prints the terminal's foreground and background colours as #RRGGBB, plus whether the background is dark.

Terminal Theme: #E5E5E5 (FG) - #000000 (BG) [Dark]
Terminal Theme: #FFFFFF (FG) - #1E1E1E (BG) [Dark]

The bracketed word at the end is the background type — the default line never prints the foreground's. Use {fg-type} in a custom format if you need it.

Platform support

Platform	Implementation	Notes
All platforms	terminaltheme.c	Escape-code query first, COLORFGBG as the fallback

This is the only terminal-related module with no per-platform source file: terminaltheme.c sits in the platform-independent part of the source list, and the two helpers it needs (ffGetTerminalResponse(), getenv()) have per-platform implementations behind a common interface. The module can still be compiled out of a build with the FF_MODULE_DISABLE_TERMINALTHEME define, which removes both the module and the display.brightColor probe described below.

Configuration

Key	Type	Default	Description
key	string	Terminal Theme	Module key. A single space hides the key and the separator
keyColor	color	–	Overrides display.color.keys
keyIcon	string	built-in glyph	Printed when display.key.type includes the icon bit. Any glyph works; "" prints none.
keyWidth	integer	–	Overrides display.key.width
outputColor	color	–	Overrides display.color.output
format	string	–	Custom output format (see below)
condition	object	–	Show the module only if the conditions match

There are no module-specific options. One environment variable changes the result:

Variable	Effect
COLORFGBG	Fallback source, formatted as <fg>;<bg> with two palette indices. Only used when the escape-code query gets no answer

Format string

Run fastfetch -h terminaltheme-format for the authoritative list.

Variable	Description
{fg-color}	Foreground colour, #RRGGBB
{fg-type}	Foreground type, Dark or Light
{bg-color}	Background colour, #RRGGBB
{bg-type}	Background type, Dark or Light

None of the four is marked * in the help output, so none is available in the key format.

{ "type": "terminaltheme", "format": "{fg-color}|{fg-type}|{bg-color}|{bg-type}" }

Terminal Theme: #FFFFFF|Light|#7F7F7F|Dark

JSON output

[
    {
        "type": "TerminalTheme",
        "result": {
            "fg": { "r": 255, "g": 255, "b": 255, "dark": false },
            "bg": { "r": 127, "g": 127, "b": 127, "dark": true }
        }
    }
]

• fg and bg are objects with four keys each, in the order r, g, b, dark.
• r / g / b are numbers 0–255; dark is a boolean.
• On failure the object carries error instead and has no result.
• Unlike the text output, the JSON keeps both dark flags, so the foreground type is available without a custom format.

Examples

// A one-line summary of both types
{ "type": "terminaltheme", "format": "fg {fg-type} / bg {bg-type}" }

// Pick a logo variant from the background
{ "type": "terminaltheme", "format": "{bg-type}" }

Pitfalls

• "Dark" in the default line describes the background only. The line ends with [%s] filled from result.bg.dark, so a light-background / dark-foreground terminal still prints [Light]. Both types are in the JSON and in the format variables.
• COLORFGBG is the fallback, not the primary source. The escape-code query (OSC 10 / OSC 11) runs first and COLORFGBG is only consulted when it gets no parseable reply — so a terminal that answers the query ignores the variable completely.
• COLORFGBG is quantised to 16 colours. Its two numbers are indices into a fixed palette, and the values in that palette are the classic X11 ones (1 is #CD0000, not #FF0000; 7 is #E5E5E5). An index outside 0–15 maps to black, and a value that does not parse as exactly two %d separated by ; is rejected outright.
• A missing COLORFGBG and an unresponsive terminal means no output. The module reports Failed to detect terminal theme through ffPrintError(), which is silent unless display.showErrors is true — the module then simply vanishes, exactly like the other terminal modules.
• The "dark" test is a luma threshold, not a perceptual one. It is r * 299 + g * 587 + b * 114 < 128000, i.e. Rec. 601 luma below 128 on a 0–255 scale. A mid-grey background around #808080 sits right at the boundary and can land either way.
• The escape query costs up to a second. ffGetTerminalResponse() waits up to FF_IO_TERM_RESP_WAIT_MS (1000 ms) for the reply, so a terminal that does not implement OSC 10 / OSC 11 delays the module by that much before falling back to COLORFGBG. The source records that Windows Terminal strips all \e from its output, which is one such case.
• The same detection also controls display.brightColor. ffOptionsInitDisplay() probes the theme with forceEnv = true — the environment path only, deliberately skipping the escape query "for performance" — and sets brightColor to false when the background is light. That happens at option-init time, whether or not the terminaltheme module is enabled, so exporting COLORFGBG changes the colours of unrelated modules.
• This module is not cached. Each call re-runs the detection, so under --dynamic-interval it re-queries the terminal on every round.

Implementation

ffDetectTerminalTheme() fills an FFTerminalThemeResult — two FFTerminalThemeColor values (uint8_t r, g, b plus a bool dark) — and then computes both dark flags. It is the only detector in this area that takes a forceEnv argument:

if (!forceEnv && detectByEscapeCode(result)) return true;
return detectByEnv(result);

ffPrintTerminalTheme() formats the default line as #%02X%02X%02X (FG) - #%02X%02X%02X (BG) [%s], or pre-renders the two #RRGGBB strings and the two type strings for the format engine. ffGenerateTerminalThemeJsonResult() writes the two nested objects.

Escape-code path

Two queries are sent back to back — \e]10;?\e\\ for the foreground and \e]11;?\e\\ for the background — and the replies are parsed as rgb:RRRR/GGGG/BBBB with %*[^0-9]10;rgb:%x/%x/%x … %*[^0-9]11;rgb:%x/%x/%x. The leading %*[^0-9] is what makes the parse tolerant of the escape sequence itself being present or stripped. Components above 0x100 — a terminal answering with 16-bit channels — make all three components of that colour be divided by 0x100.

Environment path

COLORFGBG is split with sscanf(color, "%d;%d", &f, &g), and each number goes through fgbgToColor(), a 16-entry switch over the classic ANSI palette (0 black, 1 #CD0000, 2 #00CD00, 3 #CDCD00, 4 #0000EE, 5 #CD00CD, 6 #00CDCD, 7 #E5E5E5, then the bright variants 8–15, 8 being #7F7F7F and 15 #FFFFFF). Anything outside that range becomes black.