Manufacturers of writing paper need to add mineral filler to paper pulp if the paper made from the pulp is to look white  Without such filler, paper products look grayish  To make writing paper that looks white from recycled paper requires more filler than is required to make such paper from other sources
Ttherefore, barring the more efficient use of fillers in paper manufacturing or the development of paper-whitening technologies that do not require mineral fillers, if writing paper made from recycled paper comes to replace other types of writing paper, paper manufacturers will have to use more filler than they now use
Grayish writing paper will not be a universally acceptable alternative to white writing paper.