Swift UI and shadow colors - ios

Question

So, I need a button in iOS / swift, that has outer shadow on bottom and right border, and inner shadow on top and left border. I was studying tutorials for several days, and came up with following solution that is ALMOST what I need.
internal func Setup() {
self.backgroundColor = .white
self.contentEdgeInsets = UIEdgeInsets(top: 10, left:30, bottom: 10, right: 30)
// Outer shadow
self.layer.shadowColor = UIColor(red: 0, green: 0, blue: 0, alpha: 1).cgColor
self.layer.shadowOffset = CGSize(width: 10, height: 10)
self.layer.shadowOpacity = 1.0
self.layer.shadowRadius = 6
self.layer.masksToBounds = false
self.layer.cornerRadius = self.frame.height / 2
// call to add inner shadow
self.addInnerShadow()
}
internal func addInnerShadow() {
let cornerRadius = self.bounds.height / 2
let innerShadow = CALayer()
innerShadow.frame = bounds
// Shadow path (1pt ring around bounds)
let path = UIBezierPath(roundedRect: innerShadow.bounds.insetBy(dx: -1, dy: -1), cornerRadius: cornerRadius)
let cutout = UIBezierPath(roundedRect: innerShadow.bounds, cornerRadius: cornerRadius).reversing()
path.append(cutout)
innerShadow.shadowPath = path.cgPath
innerShadow.masksToBounds = true
// Shadow properties. Color is SAME as in outer shadow, but will come out differently
innerShadow.shadowColor = UIColor(red: 0, green: 0, blue: 0, alpha: 1).cgColor
innerShadow.shadowOffset = CGSize(width: 8, height: 8)
innerShadow.shadowOpacity = 1.0
innerShadow.shadowRadius = 6
innerShadow.cornerRadius = cornerRadius
// Add
layer.addSublayer(innerShadow)
}
Function Setup() is called during button's init(), and it all creates nice shadowed button with rounded corners.
But the question is - why the top inner shadow is so light? It should be of the same color as the bottom outer shadow. If I set any other color (like red), it is always very light, with only a tint of the required color. Why? Is it possible to control the color of inner shadow as directly as I do it with outer shadow?