在webView的delegate回调方法-webViewDidFinishLoad:(UIWebView*)webView;中写上一下语句即可

//字体大小
[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.webkitTextSizeAdjust= '330%'"];
//字体颜色
[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.webkitTextFillColor= 'gray'"];
//页面背景色
[webView stringByEvaluatingJavaScriptFromString:@"document.getElementsByTagName('body')[0].style.background='#2E2E2E'"];

之前把方法写在init里怎么都不行 ，原来得写在delegate里啊 （上边的才是正确的）

self.myWebView.delegate = self;

self.myWebView.opaque = NO; //不设置这个值 页面背景始终是白色

self.myWebView.backgroundColor = [UIColor clearColor];

self.myWebView.scalesPageToFit = NO;  //禁止用户缩放页面

self.myWebView.dataDetectorTypes = UIDataDetectorTypePhoneNumber|UIDataDetectorTypeLink;

self.myWebView.scrollView.pagingEnabled = YES;

self.myWebView.scrollView.contentInset = UIEdgeInsetsMake(0, 0,0, 0);

self.myWebView.autoresizingMask = UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight;

[self.view addSubview:self.myWebView];

NSString *jsString = [[NSString alloc] initWithFormat:@"document.body.style.fontSize=%f;document.body.style.color=%@",16.0,[color webColorString]];

[self.myWebView stringByEvaluatingJavaScriptFromString:jsString];

}