Bluish Paper ???

This stamps Bluish Paper ???

Hello, identifying bluish paper is tricky and very difficult to do with images over the Internet. Here is a discussion with a bunch of information for you: https://goscf.com/t/41087

Some images for comparison------
Top Row: #357 and #358 Bluish paper Second row: #331 and #332 Normal paper--- Laid on top on an orange sheet for contrast. There is a grayish cast to the paper on the two stamps on the top row. I don't think those five-cent images you have poster are bluish paper. There is no know four-cent bluish in used condition, and I don't believe yours is on bluish paper either. Lay them upside down onto an orange or dark yellow background. If bluish papers, they will appear as a gray shade of paper. Hope this is helpful