I had a identified a 50c Malaya BMA Overprint stamp on right as possible chalky paper. The 50c was available in both ordinary and chalky.. I found stamp in the same set that was only available as Ordinary Paper per SG. I never really tried to identify it until today when I was I noticed while scanning my album pages.
Per SG, chalky paper should have a sheen when viewed off angle. I did a comparison and was able to get an angle where the right stamp was more washed out due to reflection where the stamp on left never achieved this wash out look. Yes, the lighting may think I was not "fair" to left stam but the best I could do while orienting and taking picture.
Note: Scott does not mention paper types in Classic.)