colorterm

Colorterm is an environment variable used in UNIX-like systems to indicate the color capabilities of the terminal. It is read by many programs to decide what kind of ANSI color escape sequences to emit, particularly whether the terminal supports true color (24-bit) output. Colorterm is not a formal standard, but a conventional cue used by software to tailor color rendering to the terminal’s capabilities.

Common values for colorterm point to true color support. The most widely seen value is truecolor (often exported as COLORTERM=truecolor). Other less common labels such as 24bit may appear in some environments. When colorterm indicates truecolor, applications will typically emit 24-bit color escape sequences (for example, sequences that specify exact RGB values). If colorterm is absent or set to a non-truecolor value, programs may fall back to 256-color or 16-color sequences.

Colorterm is complementary to the TERM environment variable, which describes the terminal type and its general capabilities via terminfo or termcap. Colorterm specifically signals color richness, while TERM signals functional capabilities. Because colorterm is not standardized, its presence and value can vary across terminals. Some terminals may not set it at all, or may set it inconsistently, so software often uses it as one of several signals to determine color output.

In practice, colorterm is widely used by modern terminal emulators and color-aware applications to enable true color rendering when available, enhancing color precision in prompts, syntax highlighting, and other colored output.