Brightness function

bright.rb

def bright?(color)
  if color =~ /^#([[:xdigit:]]{2})([[:xdigit:]]{2})([[:xdigit:]]{2})$/
    r = $1.to_i(16)
    g = $2.to_i(16)
    b = $3.to_i(16)

    # Use formula to calculate brightness
    # http://www.nbdtech.com/Blog/archive/2008/04/27/Calculating-the-Perceived-Brightness-of-a-Color.aspx
    brightness = Math.sqrt(r*r*0.241+g*g*0.691+b*b*0.068) / 255 * 100.0

    brightness >= 65
  else
    raise ArgumentError, "Invalid color! ('#{color}')"
  end
end