Artisteer creates a file called editor.css with all the styles for the editor. You could probably edit that and just put in what you want and delete the background color from the editor. At lest that's what I believe to be the case. We don't always know a third party software as well as the people who made it. They know it best.
This is not normal for Joomla templates. It sounds like an Artisteer problem. They probably have an answer for you since they probably have encountered it before.
Also search their forum. Here's a similar problem, a forum search will most likely give you the correct answer.
www.artisteer.com/?post_id=136457&p=forum_post Let us know if this helps.
Cheers,
ed