set image color of a template image

I have an image like this:

(Rendered as a template image)

I tried this code:

@IBOutlet weak var imgAdd: NSImageView!
imgAdd.layer?.backgroundColor = CGColor.white

Which only changes the background color of course.

Is there a way to change the color of this image programmatically?

---

So far I've tried the code below which doesn't work. (The image color doesn't change.)

func tintedImage(_ image: NSImage, tint: NSColor) -> NSImage {
    guard let tinted = image.copy() as? NSImage else { return image }
    tinted.lockFocus()
    tint.set()

    let imageRect = NSRect(origin: NSZeroPoint, size: image.size)
    NSRectFillUsingOperation(imageRect, .sourceAtop)

    tinted.unlockFocus()
    return tinted
}

imgDok.image = tintedImage(NSImage(named: "myImage")!, tint: NSColor.red)

I found the solution with everyone's help:

(Swift 3)

func tintedImage(_ image: NSImage, tint: NSColor) -> NSImage {
    guard let tinted = image.copy() as? NSImage else { return image }
    tinted.lockFocus()
    tint.set()

    let imageRect = NSRect(origin: NSZeroPoint, size: image.size)
    NSRectFillUsingOperation(imageRect, .sourceAtop)

    tinted.unlockFocus()
    return tinted
}

imgDok.image = tintedImage(NSImage(named: "myImage")!, tint: NSColor.red)

Important: in interface builder I had to set the "render as" setting of the image to "Default".