The color varieties of this Washington 2c are many and difficult to distinguish without having several of them side by side.
A color chart is useful, but an expert specialist (which I am not) would be even better.
I sometimes wonder if it really is worth trying to distinguish stamps only by color variations.
The subject and design seem much more significant, unless it’s a totally different color – like green vs blue.
So here is where you have to nit pick. I believe the stamp shown on the left (above) is the carmine and on the right is the red variety of the 1899 issue.
This stamp reportedly comes in 7 different shades – red, rose carmine, carmine, orange red, pink, vermillion, and brown orange.
Notice that the horizontal background lines do not cross the outer edges of the upper corner triangles. In earlier versions, they do cross those areas.