Install colortest by entering the following commands in the terminal:
sudo apt update sudo apt install colortest
utilities to test color capabilities of terminal
Most terminals are capable of displaying 16 colors; 8 colors and 2 different brightness values, some (like xterm) can display more, even 256 colors. . The colortest package includes set of utilities to help test how many colors a terminal can show. These color settings depend on the $TERM environment variable and termcap entry and by adjusting or selecting correct values, higher colors may be available. The following numbers of colors can be tested for: 8, 16 and 256 colors.