代码示例：（标识：css3_color_opacity）
<!DOCTYPE html>
<html>
<head>
<style>
#p1 {background-color:rgb(255,0,0);opacity:0.6;}
#p2 {background-color:rgb(0,255,0);opacity:0.6;}
#p3 {background-color:rgb(0,0,255);opacity:0.6;}
#p4 {background-color:rgb(192,192,192);opacity:0.6;}
#p5 {background-color:rgb(255,255,0);opacity:0.6;}
#p6 {background-color:rgb(255,0,255);opacity:0.6;}
</style>
</head>
<body>
<h1>用 opacity 定义颜色</h1>
<p id="p1">红色</p>
<p id="p2">绿色</p>
<p id="p3">蓝色</p>
<p id="p4">灰色</p>
<p id="p5">黄色</p>
<p id="p6">樱桃色</p>
</body>
</html>
