CALayer extension that adds borderUIColor as an attribute that can be set by key path in interface builder.

CALayer+BorderColor.swift

extension CALayer {
    
    func borderUIColor() -> UIColor? {
        return borderColor != nil ? UIColor(CGColor: borderColor!) : nil
    }
    
    func setBorderUIColor(color: UIColor) {
        borderColor = color.CGColor
    }
}