ios 生成随机颜色

- (UIColor *)randomColor {
    int R = (arc4random() % 256) ;
    int G = (arc4random() % 256) ;
    int B = (arc4random() % 256) ;
    
    return [UIColor colorWithRed:R/255.0 green:G/255.0 blue:B/255.0 alpha:1];
}