1936 University Covers

Does anyone know of a good catalogue to identify postal covers? I'm particularly interested in the blue and yellow ones and why they would be a different color.

I have about 50 from various universities, and the letters inside are discussing the exchange of bookplates with the original owner.
I guess anything is collectible!

These folks publish the catalog you'd want: https://www.upss.org/

If I understand your question, you are asking why some envelopes are on blue pape and others on yellow or cream paper.

The Post Office Department offered postal patrons a wide variety of envelopes that could be purchased with the postage paid and even a return address added. These were offered in a variety of sizes, color of envelopes, and postage provided.

One such color wall poster from 1907 that described the available envelopes at that time is shown in the link...

https://stampsmarter.org/learning/i...e_low_2f.jpg

The catalog mentioned is a detailed description of all of these envelopes

Oh that's neat! I always assumed the institutions applied the return address themselves but it was in fact a request to the post office.

I've read somewhere (probably auction block) describing, I believe it was a red paper late 1800's issue, where the price was quite high because one red envelope was created after every 500 or so regular issues.
This is just what I remember hazily so please correct me on the details.

Indeed not the case here!

Thank you classic_paper. I'm assuming we have to pay a membership fee to get the details?
$18 is not a bad yearly rate to get full catologue access if true.

You don't need to be a member, the catalog(s) and other publications are available for purchase by anyone.