通过颜色生成图片

UIColor+Image.swift

extension UIColor {
    func image(_ size: CGSize = CGSize(width: 1, height: 1)) -> UIImage {
        return UIGraphicsImageRenderer(size: size).image { (rendererContext) in
            self.setFill()
            rendererContext.fill(CGRect(origin: .zero, size: size))
        }
    }
}

Usage:

 let image0 = UIColor.orange.image(CGSize(width: 128, height: 128))
 let image1 = UIColor.yellow.image()