It's not always the case that you would choose a ramp over stairs given the choice of only one or the other. For example, there aren't many two-story homes that have a ramp leading to the second story. (Not to say they don't exist, just that they are a glaring exception.) That's what I mean by not always appropriate or desirable.

I feel I might be getting astray here. I simply think it's odd to impose on--what is as much an art form as it is a medium for communication--the restriction of only being able to use a certain color scheme. I'd be bummed out.

Luckily you don't have to sacrifice any aesthectics. SparkFun does a good job of making their stock status icons accessible by employing a combination of color and shape to help color-blind people recognize the status easier.

Here's a good example: http://www.sparkfun.com/products/10388