Colors and faces are supported in non-windowed mode, i.e., on Unix and
GNU/Linux text-only terminals and consoles, and when invoked as
‘emacs -nw’ on X, MS-DOS and MS-Windows. Emacs automatically
detects color support at startup and uses it if available. If you
think that your terminal supports colors, but Emacs won’t use them,
check the termcap entry for your display type for color-related
capabilities.
The command M-x list-colors-display pops up a window which exhibits all the colors Emacs knows about on the current display.
Syntax highlighting is also on by default on text-only terminals.
Emacs 26.1 and later support direct color mode in terminals. If Emacs finds Terminfo capabilities ‘setb24’ and ‘setf24’, 24-bit direct color mode is used. The capability strings are expected to take one 24-bit pixel value as argument and transform the pixel to a string that can be used to send 24-bit colors to the terminal.
Standard terminal definitions don’t support these capabilities and therefore custom definition is needed.
$ cat terminfo-custom.src
xterm-emacs|xterm with 24-bit direct color mode for Emacs,
use=xterm-256color,
setb24=\E[48\:2\:\:%p1%{65536}%/%d\:%p1%{256}%/%{255}%&\
%d\:%p1%{255}%&%dm,
setf24=\E[38\:2\:\:%p1%{65536}%/%d\:%p1%{256}%/%{255}%&\
%d\:%p1%{255}%&%dm,
$ tic -x -o ~/.terminfo terminfo-custom.src
$ TERM=xterm-emacs emacs -nw
Emacs 27.1 and later support Terminfo capability ‘RGB’ for detecting 24-bit direct color mode. Multiple standard terminal definitions support this capability.
$ TERM=xterm-direct infocmp | grep seta[bf]
setab=\E[%?%p1%{8}%<%t4%p1%d%e48\:2\:\:%p1%{65536}%/\
%d\:%p1%{256}%/%{255}%&%d\:%p1%{255}%&%d%;m,
setaf=\E[%?%p1%{8}%<%t3%p1%d%e38\:2\:\:%p1%{65536}%/\
%d\:%p1%{256}%/%{255}%&%d\:%p1%{255}%&%d%;m,
$ TERM=xterm-direct emacs -nw
If your terminal is incompatible with XTerm, you may have to use
another TERM definition. Any terminal whose name includes
‘direct’ should be a candidate. The toe command can be
used to find out which of these are installed on your system:
$ toe | grep '\-direct' konsole-direct konsole with direct-color indexing vte-direct vte with direct-color indexing st-direct st with direct-color indexing xterm-direct2 xterm with direct-color indexing (old) xterm-direct xterm with direct-color indexing
If Terminfo database is not available, but 24-bit direct color mode is
supported, it can still be enabled by defining the environment
variable COLORTERM to ‘truecolor’.
Terminals with ‘RGB’ capability treat pixels #000001 - #000007 as indexed colors to maintain backward compatibility with applications that are unaware of direct color mode. Therefore the seven darkest blue shades may not be available. If this is a problem, you can always use custom terminal definition with ‘setb24’ and ‘setf24’.