u/Kingpigman

I've been working on a large scale project and a large part of it is coloring the paper gray, the paper is already glued onto cardboard in a rectangular box shape and i need a lightish gray like the photo i attached, but there isint any gray paper at all in the stores near me and right now the only thing to gray stuff are pencils which dont look smooth enough, any ideas? and i dont have a high budget