When I've done faux painting, I use colors that are 2 or 3 colors apart on the painting sample card. That way you get contrast. The glaze does alter the color a little-- the one I used was white so it added white pigment to the colors -- but it helps you work with the paint. I'd try it out on a practice piece of drywall or even poster board to get the feel of it. Here's a link to decorative painting that might help -- http://www.oldhouseweb.com/stories/Detailed/12228.shtml