Setting backgroundColor of custom NSView

The correct way is

class ViewController: NSViewController {

@IBOutlet var box: NSView!

override func viewDidLoad() {
    super.viewDidLoad()
    self.view.wantsLayer = true

}

override func viewWillAppear() {
    box.layer?.backgroundColor = NSColor.blue.cgColor
    //box.layer?.setNeedsDisplay()
}

override var representedObject: AnyObject? {
    didSet {
    // Update the view, if already loaded.
    }
}}

Swift via property

extension NSView {

    var backgroundColor: NSColor? {
        get {
            if let colorRef = self.layer?.backgroundColor {
                return NSColor(CGColor: colorRef)
            } else {
                return nil
            }
        }
        set {
            self.wantsLayer = true
            self.layer?.backgroundColor = newValue?.CGColor
        }
    }   
}

Usage:

    yourView.backgroundColor = NSColor.greenColor()

Where yourView is NSView or any of its subclasses

Updated for Swift 3

extension NSView {

    var backgroundColor: NSColor? {

        get {
            if let colorRef = self.layer?.backgroundColor {
                return NSColor(cgColor: colorRef)
            } else {
                return nil
            }
        }

        set {
            self.wantsLayer = true
            self.layer?.backgroundColor = newValue?.cgColor
        }
    }
}