Yellow/Brown Tinge To Stamps

I have a sheet of 1976 Olympics 13c stamps and they have a yellow or brown tinge to them, as does the back where the gum is. Is it normal for the front and back of stamps to "age" and change colors or is this the color the front and back originally came in?

If stamps are stored improperly or subjected to a lot of light they will get a brownish tone.

Is the back (gum side) of this stamp sheet normal? Could yellowing happen just being a drawer for 40 years?

I have a 30 year old 22c Statue of Liberty sheet and the front of the stamps look pristine white, but the back has yellowing and browning.

Is a sheet still considered to be in mint condition with the gum side yellowing or browning?

Personally, I'd describe it as "unmounted mint with toning".

Suggestion:
MINT is how the stamp came from the press.
Toning will be described just that, and be gum disturbance.

I purchased these sheets on ebay and they were described as Mint, but no mention about toning of the gum.

Newbie question. Does toned gum like in the picture affect the adherence of a stamp to an envelope?

Not at all,
be careful how you store, it will stick to anything close by, if humidity softens the gum.

These were printed on at least three different paper types with two different yellow inks. The paper is not white that they are printed on. The three versions I have listed as Type 1-3 below.

Type 1 - paper is gray and the yellow ink is bright/reactive under LW. Gum tends to be lighter in color.

Type 2 - paper is light gray and the yellow ink is dull/non-reactive under LW. Gum is darker than Type 1.

Type 3 - paper is a whitish gray under and the yellow ink is dull/non-reactive under LW. Gum is darker yet than Type 1 or Type 2.

The paper colors are distinct when compared against each other under LW but how you see them might vary slightly. I have seen a number of toned sheets/plate blocks of this issue and the toning is usually not even across all the stamps. The toning also tends to show up under LW UV as a brownish tone unevenly mixed with the grayish colors in this case.

Thank you for the information on the different paper types, which explains the brown tinge on the front and the gum. Do you happen to know about #2224 Statue of Liberty 22c sheet from 1986? Was this sheet issued with dark gum or are the sheets that I have (photo below) characteristic of toning over time? Most auctions on ebay don't mention anything about gum color or toning on the gum side nor do they show photos of the gum side. What kind of feedback should I leave for toned gum on the Statue of Liberty sheets if the sheets weren't issued with toned gum? How is an average person supposed to know about the variation in paper types and gum on sheets?

Both of your sheets look perfectly normal to me - as issued from the PO. If they were described 'mint' on ebay, I would consider that an accurate description.

Gum does not have to be a pure 'white' color.

Toning is an entirely different subject - your sheets do not appear to have any toning problem - which is an environmental problem with storage etc.

An 'average' person is not supposed to know about this. (Or care, for that matter!)

Stamp collectors - and especially philatelists - read about this stuff in catalogs & books...(and online forums!!)

Yes, we do. Just yesterday I read that the gum, in some cases, can cause toning. Fourth post down.

https://goscf.com/t/65133&whichpage=1#566232