I finally mixed them up and tried them. The first two photos are the results on some sheer poly stuff. One is from the "fancy" section of the fabric store and the other is leftover from Halloween.
The fabrics are really sheer (you can see threads stuck to my design wall showing through). I think this would be fun used as a technique to put color on some kind of an overlay -- it's very subtle. I plan to experiment a bit more with these.
I have to admit, I was dismayed when I mixed up the colors -- the yellow looked kind of brownish and the blue looked purple. When I mixed the two, the color was muddy. I was pleasantly surprised at the change in color on the fabric. I have a bunch more paper painted up, so I'll be playing with it a bit more before I'm finished. I'm thinking of painting an image, then trying to transfer it.