改变Error tip的背景色.

通过设置.errorTip CSS选择器的borderColor 样式。
示例：

代码：

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/05/22/changing-the-background-color-of-an-error-tip-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Style>
        @font-face {
            src: local("Base 02");
            fontFamily: Base02Embedded;
        }

        .errorTip {
            borderColor: haloOrange;
            color: black;
            fontFamily: Base02Embedded;
            fontSize: 16;
            fontWeight: normal;
        }

        TextInput {
            errorColor: haloOrange;
        }
    </mx:Style>

    <mx:TextInput id="textInput"
            errorString="Hey, you missed a spot!" />

</mx:Application>

来自：http://blog.flexexamples.com/2008/05/22/changing-the-background-color-of-an-error-tip-in-flex/