Because red and green are commonly used in vizes and because one in ten men have red-green color blindness, it'd be helpful to have a proofing mode that shows what a Tableau worksheet looks like to colorblind viewers.
(The colorblind palette is nice, but it's possible to use red and green by varying the saturation. See http://jimw.me/TabRG)
This could be extended to show how colors would look when printed in black and white.
Adobe Illustrator does this. See Adobe Illustrator accessibility