An extension of the iOS class UIColor to provide conversion to and from HSL (hue, saturation, lightness) colors.

UIColor+HSL.swift

/// An extension to provide conversion to and from HSL (hue, saturation, lightness) colors.
extension UIColor {

    /// The HSL (hue, saturation, lightness) components of a color.
    struct HSL: Hashable {

        /// The hue component of the color, in the range [0, 360°].
        var hue: CGFloat
        /// The saturation component of the color, in the range [0, 100%].
        var saturation: CGFloat
        /// The lightness component of the color, in the range [0, 100%].
        var lightness: CGFloat

    }

    /// The HSL (hue, saturation, lightness) components of the color.
    var hsl: HSL {
        var (h, s, b) = (CGFloat(), CGFloat(), CGFloat())
        getHue(&h, saturation: &s, brightness: &b, alpha: nil)
        
        let l = ((2.0 - s) * b) / 2.0

        switch l {
        case 0.0, 1.0:
            s = 0.0
        case 0.0..<0.5:
            s = (s * b) / (l * 2.0)
        default:
            s = (s * b) / (2.0 - l * 2.0)
        }

        return HSL(hue: h * 360.0,
                   saturation: s * 100.0,
                   lightness: l * 100.0)
    }

    /// Initializes a color from HSL (hue, saturation, lightness) components.
    /// - parameter hsl: The components used to initialize the color.
    /// - parameter alpha: The alpha value of the color.
    convenience init(_ hsl: HSL, alpha: CGFloat = 1.0) {
        let h = hsl.hue / 360.0
        var s = hsl.saturation / 100.0
        let l = hsl.lightness / 100.0

        let t = s * ((l < 0.5) ? l : (1.0 - l))
        let b = l + t
        s = (l > 0.0) ? (2.0 * t / b) : 0.0

        self.init(hue: h, saturation: s, brightness: b, alpha: alpha)
    }

}

Great! Thanks a lot!