colors256.rb

#!/usr/bin/ruby

256.times do |color|
  if color < 7 || (color > 15 && (color - 16) % 36 < 18)
    fg = 231
  else
    fg = 0
  end

  print "\e[38;5;#{fg};48;5;#{color}m #{color.to_s.rjust(3)} \e[m"

  if (color >= 15 && color < 232 && (color - 15) % 18 == 0) || (color > 231 && (color - 15) % 12 == 0)
    puts
  end

  puts if color == 15 || color == 231
end

puts