This is a topic I planned to post on for some time and I final got some time to do so. I like to collect modern US issues because there are so many potential varieties to find, many not documented that I am aware of. What I planned to cover is considered a specialists area by many, including by Scott. Don't let that scare you off as it is an easy to one get into.
I have been working to document the various paper types modern stamps are printed on for the Stampsmarter US Tagging & Luminescence Database. This involves using a LW UV (black light) to check the luminescence of the paper. For those not familiar a simplified example would be hi-bright versus non-brite, but that in not the subject at hand. You can learn more at the Stampsmarter site.
In hunting down and trying to document the various paper types, one thing I found is that there are many US issues of the same stamp where they have been printed with both a luminescent and non-luminescent ink(s). A small percentage of what I have found are noted in various places, but most I have not seen or found any reference to. If references exist, I would be interested in knowing of them. Scott Specialist Catalog does list a handful in a note with the stamp. I have not found references to any of these.
Now what you have been waiting for if you read this far. This is just a sampling of some of them. Note, while many below are shown used, I have confirmed they exist by finding mint examples. All images below are under LW UV.
#1550 this one can be found in a wide variety of variations.
#1895 quite dramatic difference.
#2030a one of my favorites since there are many dramatic tagging freaks.
#2045 notice the medals.
#2399 I have found mint plate blocks of both varieties and included a side by side comparison of the color bars as well.
#2426 numerous variation in the the level of luminescence.
#2533 the image below doesn't do the bright orange color justice, it is very vivid.
Finally #3522 notice the color on the side of the vehicles.
Some key words you can use to search with on the Stampsmarter tagging DB are "luminescent ink", "reactive" or "non-reactive". This will bring up some of the paper types as well. Once you see for example a non-reactive ink variety show up you have interest in, do another search with the Scott # to see or getting listings for the various varieties. I hadn't expected to find so many varieties or I would have included a better key word search identifier. A task for the future.
If people know of others I haven't found or listed yet, please post so I can add to DB.