Just copy/paste lines 5-17 in your shell to run this

truecolortest.sh

# If truecolor is enabled, this will return a full color spectrum
# If not, it'll just print 16 colors
# function kuler() {
  awk 'BEGIN{
    s="/\\/\\/\\/\\/\\"; s=s s s s s s s s;
    for (colnum = 0; colnum<77; colnum++) {
      r = 255-(colnum*255/76);
      g = (colnum*510/76);
      b = (colnum*255/76);
      if (g>255) g = 510-g;
      printf "\033[48;2;%d;%d;%dm", r,g,b;
      printf "\033[38;2;%d;%d;%dm", 255-r,255-g,255-b;
      printf "%s\033[0m", substr(s,colnum+1,1);
    }
    printf "\n";
  }'
# }