When I have a thick document to photocopy with several attachments I use this yellowish paper to separate them and print (via PC) the Label: Attachment 1 2 etc. That way when I print copies I can substitute the yellow printed page as a separator and it won't show up as dark if I used a different color to make a photocopy
I often use the gray paper when printing papers for my 4-H club. I was out completely of this color when I recently printed our annual booklet that I use several colors in to make sections stand out and easy to locate a different topic.