Javascript更改事件目标不透明度

Question

我尝试使用此代码将不透明度更改为0.7：

//if div hasn't been mouseovered
if(!e.target.getAttribute('data-shade'))
    e.target.style.background = color;
    e.target.setAttribute('datashade', 1);
//else div has been mouse overed
else
    e.target.style.cssText = 'opacity: 0.7';

为什么变白了？

*对不起英语不好