Example:

The scrollbar has a orange color. You change the colors as per your taste. 

<STYLE>
<!--  
BODY { scrollbar-3d-light-color: #ff9900;
           scrollbar-arrow-color: #000000;
           scrollbar-base-color: red;
           scrollbar-dark-shadow-color: #FF9900;
           scrollbar-face-color: #FF9900;
           scrollbar-highlight-color: #FF9900;
           scrollbar-shadow-color: red
}
-->
</STYLE>
For more information check out the MSDN reference for each property.