I'm pretty sure the symbol is going to be changed per set, there are a few comments to that effect on the website at least... Best bet, if you are looking for something other than color, would be shape of the icon. rounds are common, squares are uncommon, triangles rare or something along those lines...

So -- as one of those colorblind people -- it's going to be really difficult until there is a symbol of some sort. Basically, even if I can see a DIFFERENCE in the color, I still can't describe/understand it very well. Green and yellow (for me, at least), are interchangeable, often, so -- although I can tell them apart, they're really just shades of the same color. So -- never mind changing the colors, just have different symbols, that's all I ask .

Shape would help, I constantly get confused thinking black is common as in magic and have snubbed offers only to realize later they were not insults as several commons for a rare. Someone suggested a yellow orange red color set, which as prismatic shift for rareness does make sense also. The colors need to all be unique to the game.