uicolor 转成 hex 16进制色值

- (NSString *)hexStringFromColor:(UIColor *)color {
    const CGFloat *components = CGColorGetComponents(color.CGColor);
    
    CGFloat r = components[0];
    CGFloat g = components[1];
    CGFloat b = components[2];
    
    return [NSString stringWithFormat:@"#%02lX%02lX%02lX",
            lroundf(r * 255),
            lroundf(g * 255),
            lroundf(b * 255)];
}