The W3C's suggested color contrast algorithm

contrast.coffee

# http://www.w3.org/TR/AERT#color-contrast

getBrightness = (rgb) ->
  sum = parseInt(rgb[0])*299 + parseInt(rgb[1])*587 + parseInt(rgb[2])*114
  brightness = Math.round(sum / 1000) # 0 (dark) to 255 (light)

colorDifference = (a, b) ->
  max = Math.max
  min = Math.min
  d0 = max(a[0], b[0]) - min(a[0], b[0])
  d1 = max(a[1], b[1]) - min(a[1], b[1])
  d2 = max(a[2], b[2]) - min(a[2], b[2])
  d0+d1+d2

colorContrast = (a, b) ->
  b0 = getBrightness(a)
  b1 = getBrightness(b)
  contrast =
    brightness: Math.abs(b0-b1)
    difference: colorDifference(a, b)
  contrast

hasEnoughContrast = (a, b) ->
  contrast = colorContrast(a, b)
  contrast.brightness > 125 and contrast.difference > 500

##

one = [0, 0, 0]
two = [255, 255, 255]
console.log hasEnoughContrast(one, two)