determine if light or dark foreground is better for a given background color

color.swift

    // inspiration: https://stackoverflow.com/a/3943023/558780

    // wc3 approach
    public static func favorsDarkForeground(_ bgColor: UIColor) -> Bool {
        
        if let rgb = bgColor.rgb() {
            
            var uicolors: Array<Float> = [Float(rgb.red) / 255, Float(rgb.green) / 255, Float(rgb.blue) / 255];
            var c = uicolors.map({ (uicolor) -> Float in
                if (uicolor <= 0.03928) {
                    return uicolor / 12.92
                }
                return pow(((uicolor + 0.055) / 1.055), 2.4)
            })
            var L = (0.2126 * c[0]) + (0.7152 * c[1]) + (0.0722 * c[2])
            return L > 0.179
        } else {
            print("could not get rgb values")
            return false
        }
    }

    // simpler (in some cases better results)
    public static func  favorsDarkForeground2(_ bgColor: UIColor) -> Bool {
        if let rgb = bgColor.rgb() {
            return (((Float(rgb.red) * 0.299) + (Float(rgb.green) * 0.587) + (Float(rgb.blue) * 0.114)) > 186)
        } else { 
            return false
        }
    }

extension UIColor {

    func rgb() -> (red:Int, green:Int, blue:Int, alpha:Int)? {
        var fRed : CGFloat = 0
        var fGreen : CGFloat = 0
        var fBlue : CGFloat = 0
        var fAlpha: CGFloat = 0
        if self.getRed(&fRed, green: &fGreen, blue: &fBlue, alpha: &fAlpha) {
            let iRed = Int(fRed * 255.0)
            let iGreen = Int(fGreen * 255.0)
            let iBlue = Int(fBlue * 255.0)
            let iAlpha = Int(fAlpha * 255.0)

            return (red:iRed, green:iGreen, blue:iBlue, alpha:iAlpha)
        } else {
            // Could not extract RGBA components:
            return nil
        }
    }
}