Surely you have came through a myriad of sites with a customized scrollbars that have colors suiting those of the site, here is the trick how to obtain that effect with simple Cascading Style Sheets (CSS):

BODY {SCROLLBAR-FACE-COLOR: #cccccc; SCROLLBAR-HIGHLIGHT-COLOR: #161616; SCROLLBAR-SHADOW-COLOR: #000000; SCROLLBAR-3DLIGHT-COLOR: #000000; SCROLLBAR-ARROW-COLOR: #333333; SCROLLBAR-TRACK-COLOR: #999999; SCROLLBAR-DARKSHADOW-COLOR: #000000; overflow: auto }
 

Just change the colors to suit your needs.