I've been looking at a 2c Perry Davis and my first thought is that it is the Brown Red variety (RS76) but though the color is a bit faded, it really doesn't have any red. The stamp in question is the one in the middle. The right and left RS76s show a definite tint of red.
I know it can be tough to tell from a scan, but the difference is present in person in daylight. Is the middle stamp just faded, or minor shade difference of the Brown Red, or could it be something else?
The Perry Davis issues were printed in many colors including Brown for the 4c and the 2c on silk paper. My 4cs are pretty fresh and are tough to compare. The 2c Brown is unique so doubt I will ever see that one!