I have the following code:

<SELECT id="HtmlList" name="HtmlList[]" style="OVERFLOW: auto; WIDTH: 400px; HEIGHT: 25px;" size="6" MULTIPLE>
</SELECT>

How do I format the background colour when an item is selected?

<SELECT id="HtmlList" name="HtmlList[]" style="OVERFLOW: auto; WIDTH: 400px; HEIGHT: 25px; background-color:COLOR HERE;" size="6"MULTIPLE><option value="option value" name="yourname" style="background-color:COLOR HERE; color:FONT COLOR;">Option Text</option></SELECT>