<style type="text/css">
html{scrollbar-track-color:orange;}
body{scrollbar-track-color:red;}
textarea{scrollbar-track-color:blue;}
div{
scrollbar-track-color:green;
overflow:scroll;
width:200px;height:150px;
border:1px solid red;
}
</style>
...
<body>
<form action="formular.php">
<textarea rows="10" cols="40">
Beispieltext
</textarea>
</form>
<div>div-Container</div>