An extension of the iOS class UIColor to provide conversion to and from YPbPr colors.

UIColor+YPbPr.swift

/// An extension to provide conversion to and from Y′PbPr colors.
extension UIColor {
    
    /// The Rec.601 (standard-definition) coefficients used to calculate luma.
    private static let encoding: (r: CGFloat, g: CGFloat, b: CGFloat) = (0.299, 0.587, 0.114)

    /// The Y′PbPr components of a color - luma (Y′) and chroma (Pb,Pr).
    struct YPbPr: Hashable {

        /// The luma component of the color, in the range [0, 1] (black to white).
        var Y: CGFloat
        /// The blue-difference chroma component of the color, in the range [-0.5, 0.5].
        var Pb: CGFloat
        /// The red-difference chroma component of the color, in the range [-0.5, 0.5].
        var Pr: CGFloat

    }

    /// The Y′PbPr components of the color using Rec.601 (standard-definition) encoding.
    var yPbPr: YPbPr {
        var (r, g, b) = (CGFloat(), CGFloat(), CGFloat())
        getRed(&r, green: &g, blue: &b, alpha: nil)

        let k = UIColor.encoding
        let Y = (k.r * r) + (k.g * g) + (k.b * b)
        let Pb = 0.5 * ((b - Y) / (1.0 - k.b))
        let Pr = 0.5 * ((r - Y) / (1.0 - k.r))

        return YPbPr(Y: Y, Pb: Pb, Pr: Pr)
    }

    /// Initializes a color from Y′PbPr components.
    /// - parameter yPbPr: The components used to initialize the color.
    /// - parameter alpha: The alpha value of the color.
    convenience init(_ yPbPr: YPbPr, alpha: CGFloat = 1.0) {
        let Y = yPbPr.Y
        let Pb = yPbPr.Pb
        let Pr = yPbPr.Pr

        let k = UIColor.encoding
        let kr = (Pr * ((1.0 - k.r) / 0.5))
        let kgb = (Pb * ((k.b * (1.0 - k.b)) / (0.5 * k.g)))
        let kgr = (Pr * ((k.r * (1.0 - k.r)) / (0.5 * k.g)))
        let kb = (Pb * ((1.0 - k.b) / 0.5))

        let r = Y + kr
        let g = Y - kgb - kgr
        let b = Y + kb

        self.init(red: r, green: g, blue: b, alpha: alpha)
    }

}

The digital equivalent of YPbPr is YCbCr defined here: https://gist.github.com/adamgraham/0807893f1721056b279b40d3bd4e1e96