Like for neopets, how?

As far as I'm concerned (and from the last time I went on Neopets) you can't do that with the restrictions the staff has there. I may be wrong, and this should be in the Neopets section.

Using css! You can either use this code:

<style type="text/css">
body { scrollbar-base-color:#000000}
</style>

or this one is which you get to be specific about everything:

<style type="text/css">
body
{ scrollbar-face-color : #000000;
scrollbar-highlight-color : #000000;
scrollbar-3dlight-color : #000000;
scrollbar-shadow-color : #000000;
scrollbar-darkshadow-color : #000000;
scrollbar-track-color : #000000;
scrollbar-arrow-color : #000000; }
</style>

Just change the #000000 to the color of your choice.

Scrollbars do work in Neopets, but aren't supported by Firefox.