RGB颜色文字与UIColor初始化相同：

#colorLiteral(red: 1,green: 1,blue: 1,alpha: 1)

或者您可以选择键入Image Literal的颜色。

您也可以使用扩展名以十六进制颜色代替输入rgba值

extension UIColor {

    convenience init(hexString: String,alpha: CGFloat = 1.0) {
        let hexString: String = hexString.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
        let scanner = Scanner(string: hexString)
        if (hexString.hasPrefix("#")) {
            scanner.scanLocation = 1
        }
        var color: UInt32 = 0
        scanner.scanHexInt32(&color)
        let mask = 0x000000FF
        let r = Int(color >> 16) & mask
        let g = Int(color >> 8) & mask
        let b = Int(color) & mask
        let red   = CGFloat(r) / 255.0
        let green = CGFloat(g) / 255.0
        let blue  = CGFloat(b) / 255.0
        self.init(red:red,green:green,blue:blue,alpha:alpha)
    }
    func toHexString() -> String {
        var r:CGFloat = 0
        var g:CGFloat = 0
        var b:CGFloat = 0
        var a:CGFloat = 0
        getRed(&r,green: &g,blue: &b,alpha: &a)
        let rgb:Int = (Int)(r*255)<<16 | (Int)(g*255)<<8 | (Int)(b*255)<<0
        return String(format:"#%06x",rgb)
    }

}

然后您可以使用以下代码进行编码：

self.backgroundColor = UIColor(hexString: "#4A4A4A")