设置iphone中的UIToolbar的颜色

在ios4.3以上版本，想把UIToolbar的颜色改成灰色，

但是下面的代码没有实现：

- (void)drawRect:(CGRect)rect {

    UIGraphicsBeginImageContext(rect.size);

    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSaveGState(ctx);

        [[UIColor colorWithRed:64.0f/255.0f
                         green:64.0f/255.0f
                          blue:64.0f/255.0f
                         alpha:1.0f] set];

    CGRect myRect = CGRectMake(0, 0, self.frame.size.width, self.frame.size.height);
    CGContextFillRect(ctx, myRect);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    CGContextRestoreGState(ctx);
    UIGraphicsEndImageContext();

    [image drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];
}

为什么？