Cavalry in the German Army were issued the 1911 pattern ammunition pouch in sets of two. Unlike the infantry pattern that held 60 cartridges in five-round stripper clips, the cavalry pattern held 30 cartridges. Like almost all leather equipment, the 1911 pattern ammunition pouch was originally manufactured in a light honey-brown color that was fairly conspicuous on the battlefield. In response to this problem, in March 1915 the Prussian War Ministry issued an order directly that all leather equipment was to be “blackened”. The Bavarian War Ministry did not issue a similar order until March 1916.
Blackening was usually done with either shoe polish, dye, or even motor oil on occasion. It appears that the blackening order was carried out somewhat unevenly and in some instances even ignored- it pretty much was subject to the whim/interest of the local commanders and it would appear that some were fairly lax in this regard. Also, from the evidence, it does not appear that the leather was actually dyed black when manufactured and there are examples made in 1918 that are a medium brown. Most surviving examples appear to be dark brown which would suggest some fading over time.
Below are some examples of various 1911 Ammunition Pouches:

An excellent example of a 1911 pattern ammunition pouch that was “blackened” and later faded a bit with age.

An example of the 1911 pattern ammunition pouch that was manufactured in 1918. Note that this is in a medium brown.

From the issue stamps, it appears that this set of pouches were issued in 1915 to the 8 Kurassier Regiment.
While by no means will this settle the “blackening controversy”, at least it does put some samples out there for discussion. I do believe that the “blackening” that was used is not like the complete “pure” dye that you see with German WWII ammunition pouches. It’s interesting that even in 1918, manufacturers were still making these in a medium to dark brown (depending on the light, it would seem); so far I have yet to see a set of pouches that were manufactured in complete black and it’s obvious that the blackening agent was some sort of a wash.
I hope this has helped. 🙂
Horrido!