After hearing the teak stock story for so long, trying to find out what one looked like, I inquired and asked around. This is the e-mail I got regarding the subject.
This is from Matt Shuster, owner of Ironwood Designs.

Carl,
My sincerest apologies for the delay in responding.
Ok, so first off, Teak was never used for any Yugo rifle stocks.
You assessment is correct, as it would be unreasonable to use a southeastern Asian expensive wood for
military issue arms.
We had actually used Teak for our early production Yugo stocks, as we had been misinformed years ago that Teak was the original material
used for the stocks. Looking at the early Mitchell arms imports, they did very much have a color similar to Teak.
Years later, I had spoken to someone at Potomac Arms, and we had the very same conversation regarding wood types.
He said that he had a conversation with a person at Zastava about what wood they actually used.
They laughed when he had asked about Teak, and made the comment that why would they import expensive
semi exotic woods for their rifle stock manufacturing. He said that the wood used was an Eastern European species of
Birch that was used for the M70 series of rifles, ( M70 M72 M76 etc..) Beech was used on the M90 series, and is currently
used on the recent M85 Yugos.
We used Teak initially because the color looked very much like those early Mitchell imports, but then stopped after the
price of Teak became far too expensive. We still offer Afromosia because it has the persimmon like color found on the Early imports.
Personally, I do not know of that color is what the raw wood looks like, or if it was the finish/stain that was applied to the original stocks.
I haven't taken an original Yugo stock part and sanded it down raw to see the original wood color. Or at least, I have not done
that in a while.
Hardwood American Birch is one of the woods we often use for Yugo stocks. It can be stained/dyed, with a little experimentation,
to closely match those nice early Mitchell stocks. Most of the surplus stocks that I have seen over the past several years, have been
the torn up battle used parts, that are typically super dark and dirty from grime, and most likely over coats of a darker oil/preservative.
I hope this will help settle any misunderstandings about what they actually used.
I have no problem with you posting this for public view.
Thanks,
Matt
IWD
For more information about our products, please visit our web site.
www.Ironwooddesigns.com
We used Teak initially because the color looked very much like those early Mitchell imports
Mitchell imports, Hhuuummmmm?
So, it seems Mitchell imports doctored up and/or mis-lead/misrepresented their products with information on these as well. Which, it seems in my years of collecting, is a typical complaint of them, even to this day.
So after looking for a bit, I find this:

Now the basic teak myth was, "stocks were made of teak to resist rot in humid/wet jungle settings" But according to:
English Elm | Baldwin Hardwoods
The wood is also resistant to decay when permanently wet, and hollowed trunks were widely used as water pipes during the medieval period in Europe. Elm was also used as piers in the construction of the original London Bridge.
So, elm was used in the construction of a bridge, and water piping, so it should have no issues handling a jungle setting.
But, like any untreated wood left in contact or lying on the ground, it will deteriorate and become food for fungus or insects, given enough time, teak will also deteriorate in the same equal conditions. This type of destruction can be found on any type jungle bringback that was not sufficiently protected, "no" untreated wood is really immune to contact with the earth and nature.
Everything, is showing with teak wood.

I'm not going to get into a pissing/bashing contest here, but, I wonder if this is were this myth originated. I mean, Zastava, the ones who made these weapons, said nope, no teak was used.
One thing that may explain the different stocks, Yugoslavia seemed to use two styles of wood harvesting at the mill, straight cut and rift cut. This one trait can even be seen on Yugoslavian Mausers. along with using woods like beech, birch, elm and walnut, but again, no teak. A straight cut produces a normal grain pattern, the stock grain could possibly look like a typical beech/birch, but, it still could be made from elm. A rift cut would produce a larger different grain pattern from, even if cut from the same log as a straight cut, simply due to the way the log is cut, This is this is the style it seems, a majority of Yugoslavian SKSs display.
So in theory, it should work out in this fashion..
Straight cut elm or they could have possibly used birch, Yugoslavian M59 stock:
The wood is so dark from use, most of the grain features are hidden.

This shows the difference in the two woods, obviously a typical elm rift cut hand guard, with the wood/grain difference of the stock
Rift cut Yugoslavian M59 elm stock:
