Darken color

darkenColor.swift

func darkenColor(color: NSString, amount: Float) -> (hexColor: String, color: NSColor) {
  let originalRed = Float(Int(color.substringWithRange(NSRange(location: 0, length: 2)), radix: 16)!)
  let originalGreen = Float(Int(color.substringWithRange(NSRange(location: 2, length: 2)), radix: 16)!)
  let originalBlue = Float(Int(color.substringWithRange(NSRange(location: 4, length: 2)), radix: 16)!)
  
  let valueRed = originalRed * amount
  let darkenRed = String(format: "%02X", Int(valueRed))
  
  let valueGreen = originalGreen * amount
  let darkenGreen = String(format: "%02X", Int(valueGreen))
  
  let valueBlue = originalBlue * amount
  let darkenBlue = String(format: "%02X", Int(valueBlue))
  
  return (
    "#\(darkenRed)\(darkenGreen)\(darkenBlue)",
    NSColor(
      red: CGFloat(Int(darkenRed, radix: 16)!)/255,
      green: CGFloat(Int(darkenGreen, radix: 16)!)/255,
      blue: CGFloat(Int(darkenBlue, radix: 16)!)/255,
      alpha: 1.0
    )
  )
}