shadeColor

extension UIColor {
	
	func shadeColor(factor: CGFloat) -> UIColor {
		
		var r: CGFloat = 0
		var g: CGFloat = 0
		var b: CGFloat = 0
		var a: CGFloat = 0
		
		var t: CGFloat = factor < 0 ? 0 : 1
		var p: CGFloat = factor < 0 ? -factor : factor
		
		getRed(&r, green: &g, blue: &b, alpha: &a)
		
		r = (t-r)*p+r
		g = (t-g)*p+g
		b = (t-b)*p+b
		
		return UIColor(red: r, green: g, blue: b, alpha: a)
		
	}
}