# File lib/ansi/code.rb, line 336
    def rgb_256(r, g, b)
      # TODO: what was rgb_valid for?
      #r, g, b = [r, g, b].map{ |c| rgb_valid(c); (6 * (c.to_f / 256.0)).to_i }
      r, g, b = [r, g, b].map{ |c| (6 * (c.to_f / 256.0)).to_i }
      v = (r * 36 + g * 6 + b + 16).abs
      raise ArgumentError, "RGB value is outside 0-255 range -- #{v}" if v > 255
      v
    end