The others are all more knowledgeable than I am with color paper and chemistry but, as a side note, whenever I am testing paper for fog or chemistry problems, I like to cut/tear a sheet of paper in half then develop one half, unexposed, and make a photogram on the other half.
The reason for this is because I want to see if the paper gets black where it's supposed to be black and stays white where it's supposed to be white. The other half, unexposed, tells me if there is overall fogging or other problems with the paper.
I suppose I could to the same test with two sheets of paper, making a photogram on one and no exposure on the other but I like to conserve my resources.