NSImage Mask image with NSColor (Swift)

gistfile1.txt

        func mask(color: NSColor) -> NSImage {
            
            let imageRect           = CGRect(x: CGFloat(0.0), y: CGFloat(0.0), width: CGFloat(self.size.width), height: CGFloat(self.size.height))
            var newImage:NSImage?   = nil
            
            let context = IOSXGraphicsBeginImageContextWithOptions(imageRect.size, false, 1.0)
            context.clip(to: imageRect, mask: self.cgImage!)
            context.setFillColor(color.cgColor)
            context.setBlendMode(.difference)
            context.fill(imageRect)
            
            newImage = IOSXGraphicsGetImageFromImageContext(context)
            return newImage!
        }