Any thought about transparency?
What about other CSS font features: line-height, letter spacing, etc?
What about having a first step: select your units. So people can have everything based off pixels, em, whatever.
What about sub-submenus? Any way to expand that? I think sometimes those can be appropriate.
Super cool feature would be the ability to create basic graphics, like gradients. This would most likely be a v2.0 feature.
Just some ideas!