... and there in the jungle sat Tarzan painting white stripes on black zebras, or was he painting black stripes on white zebras, or was he painting black and white stripes on clear zebras?
I have been intrigued by this thread, since it is wholly a matter of preference to each collector. As a postal history collector, I am not as fond of mounting lots of individual stamps on a page - and especially remounting when I want to make a text change. For me, clear mounts didn't define the perforations or centering very well, and black mounts made it look like a mourning exhibit. (What color of mounts do you use for mourning stamps?) Re-mounting also wasted a lot of mounts and time.
I selected something in between and took a lesson from exhibiting to matte an item. Here is a quick sample page I made up a few minutes ago for a 1-frame exhibit I am working on with the dry-print postage dues of the late 1950s. The blocks are in mounts on a fairly neutral colored card stock, which can then be applied to the page of text with your choice of adhesive. The neutral color shows the perforations and centering better than white, but not as starkly as black would. When I change the text, I move the entire matte over and re-stick it to the new page.
Yes, I could achieve the same contrast with only a neutral colored page, but the additional point of the matte concept means little remounting.