Stylus color mixing mixin

gistfile1.txt

/**
 * Colour mixer: mix source with a target colour by a % value
 */

mix(source, target, ammount)

  ammount = unit(ammount, '%')

  unless source is a 'rgba' and target is a 'rgba'
    error('mix() expects rgb colour values')

  rs = red(source)
  gs = green(source)
  bs = blue(source)

  rt = red(target)
  gt = green(target)
  bt = blue(target)

  ammount-s = (100 - ammount) / 100
  ammount-t = ammount / 100

  r = round((rs * ammount-s) + (rt * ammount-t))
  g = round((gs * ammount-s) + (gt * ammount-t))
  b = round((bs * ammount-s) + (bt * ammount-t))

  rgb(r,g,b)