black_or_white.rb

# takes a hex value of a colour (0xffffff) and returns either black or white, which ever is easier to see  

def black_or_white(hex)
  rgb = {}
  %w(r g b).inject(hex) {|a,i| rest, rgb[i] = a.divmod 256; rest}

  r = rgb['r']/255      
  g = rgb['g']/255      
  b = rgb['b']/255      

  [r, g, b].max > 0.55 ? "#000000" : "#FFFFFF"
end