COLORTERM
also: COLORTERM environment variable
An environment variable that indicates a terminal emulator supports color output. When set, it tells applications they can safely use colored text and escape sequences.
COLORTERM is an environment variable that signals whether a terminal supports color display. When present and set to a non-empty value, it tells command-line programs and shell utilities that 256-color or truecolor output is available.
Common values include truecolor (24-bit RGB color), 256color (256-color palette), or simply any non-empty string. For example, modern terminals like GNOME Terminal, Konsole, and iTerm2 automatically set this variable when launched.
Applications like less, vim, and grep check this variable to decide whether to use colored output. Without it set, these tools may disable colors even if the terminal supports them, resulting in plain monochrome output.