xterm256color

Xterm256color is a terminfo capability and a widely adopted terminal type for 256-color support in terminal emulators such as xterm and its derivatives. It is commonly exposed to applications by setting the TERM environment variable to xterm-256color, allowing programs to select colors from a 256-color palette. Many modern terminal applications and build tools rely on this designation to enable richer color output.

The 256-color palette is divided into three groups. The first 16 colors (0–15) provide the standard eight colors and their bright variants. The next 216 colors (16–231) form a 6×6×6 color cube, with each color component using one of six levels: 0, 95, 135, 175, 215, and 255. A color’s index is computed as 16 + 36·r + 6·g + b, where r, g, and b are 0–5. The final 24 colors (232–255) are grayscale values, ranging from 8 to 238 in steps of 10.

Terminals supporting xterm-256color use ANSI SGR escape sequences to choose colors. For example, 38;5;n selects a specific foreground color n, and 48;5;n selects a background color n. Color numbers corresponding to 196 represent a bright red, while other numbers map to the cube and grayscale ranges.

Compatibility notes indicate that xterm-256color denotes 256-color capability, not true color. While many terminals also support true-color (24-bit) output, xterm-256color remains common for backward compatibility and performance. Terminfo entries for this capability define color support and the associated setaf/setab sequences used by text-based applications.