24 bit color (truecolor)

Delta looks best if your terminal application supports 24 bit colors. See https://github.com/termstandard/colors#readme. For example, on MacOS, iTerm2 supports 24-bit colors but Terminal.app does not.

If your terminal application does not support 24-bit color, delta will still work, by automatically choosing the closest color from those available. See the Colors section of the help output below.

If you're using tmux, it's worth checking that 24 bit color is working correctly. For example, run a color test script like this one, or one of the others listed here. If you do not see smooth color gradients, see the discussion at tmux#696. The short version is you need something like this in your ~/.tmux.conf:

set -ga terminal-overrides ",xterm-256color:Tc"

and you may then need to quit tmux completely for it to take effect.

True color output in GNU Screen is currently only possible when using a development build, as support for it is not yet implemented in the (v4) release versions. A snapshot of the latest Git trunk can be obtained via https://git.savannah.gnu.org/cgit/screen.git/snapshot/screen-master.tar.gz - the required build steps are described in the src/INSTALL file. After installing the program, 24-bit color support can be activated by including truecolor on in either the system's or the user's screenrc file.