Blending two UIColor's. Swift implementation of JordanDelcros's JS algorithm https://gist.github.com/JordanDelcros/518396da1c13f75ee057

UIColor+Blend.swift

import UIKit

public extension UIColor {
    
    /**
     Blend current color with some overlay
     
     Source - [JordanDelcros's JS algorithm](https://gist.github.com/JordanDelcros/518396da1c13f75ee057)
     */
    func blended(with overlay: UIColor) -> UIColor {
        let base = self.components
        let overlay = overlay.components
        let resultAlpha = 1 - (1 - overlay.alpha) * (1 - base.alpha)
        let blendComponents = { (baseComponent: CGFloat, overlayComponent: CGFloat) -> CGFloat in
            (baseComponent * base.alpha * (1 - overlay.alpha) / resultAlpha) + (overlayComponent * overlay.alpha / resultAlpha)
        }
        return UIColor(
            red: blendComponents(base.red, overlay.red),
            green: blendComponents(base.green, overlay.green),
            blue: blendComponents(base.blue, overlay.blue),
            alpha: resultAlpha
        )
    }
    
    var components: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) {
        var red: CGFloat = 0
        var green: CGFloat = 0
        var blue: CGFloat = 0
        var alpha: CGFloat = 0
        getRed(&red, green: &green, blue: &blue, alpha: &alpha)
        return (red, green, blue, alpha)
    }
    
}