a port of 256colors.pl in lua see: xterm's folder

256colors.lua

opt_h, opt_q, opt_r = false, false, false

function map_cube(v)
   if opt_r then return 5 - v end
   return v
end
function map_gray(v)
   if opt_r then return 23 - v end
   return v
end

if opt_q then io.write("\x1b]4") end
-- colors 16-231 are a 6x6x6 color cube                                                                                    
for red = 0, 5 do
   for green = 0, 5 do
      for blue = 0, 5 do
         if not opt_q then io.write("\x1b]4") end
         io.write(string.format(";%d;rgb:%2.2x/%2.2x/%2.2x",
                             16 + (map_cube(red) * 36 ) + (map_cube(green) * 6) + map_cube(blue),
                             not red == 0 and red * 40 + 55 or 0,
                             not green == 0 and green * 40 + 55 or 0,
                             not blue == 0 and blue * 40 + 55 or 0))
         if not opt_q then io.write("\1xb\\") end
      end
   end
end

-- colors 232-255 are a grayscale ramp, intentionally leaving out                                                          
-- black and white                                                                                                         
for gray = 0, 23 do
   level = map_gray(gray) * 10 + 8
   if opt_q then io.write("\x1b]4") end
   io.write(string.format(";%d;rgb:%2.2x/%2.2x/%2.2x",
                       232 + gray, level, level, level))
   if opt_q then io.write("\x1b\\") end
end
if opt_q then io.write("\x1b\\") end

-- display the colors    


-- first the system ones:                                                                                                  
io.write("System colors:\n")
for color = 0, 7 do
   io.write(string.format("\x1b[48;5;%sm  ", color))
end
io.write("\x1b[0m\n")
for color = 8, 15 do
   io.write(string.format("\x1b[48;5;%sm  ", color))
end
io.write("\x1b[0m\n\n")

-- now the color cube                                                                                                      
io.write("Color cube, 6x6x6:\n")
for green = 0, 5 do
   for red = 0, 5 do
      for blue = 0, 5 do
         color = 16 + red * 36 + green * 6 + blue
         io.write(string.format("\x1b[48;5;%sm  ", color))
      end
      io.write("\x1b[0m ")
   end
   io.write("\n")
end

-- now the grayscale ramp                                                                                                  
print("Grayscale ramp:")
for color = 232, 255 do
   io.write(string.format("\x1b[48;5;%sm  ", color))
end
io.write("\x1b[0m\n")