An update from Brian:

Paco Rivas responded first.  He said :

I was speaking with a former Bücker mechanic about it and he told me: “Se usaba para identificar el tipo de aceite hidráulico del amortiguador“. 
 
In English: “Used to identify the type of hydraulic oil in the shock absorber.”
 
The mechanic also told me in the beginning there were two types of hydraulic oils and the label was used to mark which one was to be used to avoid using the wrong one.  Later, only one type was used.  

Joe Vasile responded with more information and pictures of the old original landing gear leg fabric from his Jungmann.  The fabric did not have the colored triangles, but rather stenciled triangles with AAF 3580 written on the inside.





Joe clarified that AAF 3580 corresponds to the red hydraulic fluid commonly used today.  
 
I found a picture of a Jungmann from Grenada, 1968.  It has the triangular marking.



From the same batch of photographs is E3B-336 with the same triangle.



I’m still hoping someone can produce a good, clear picture of the marking.



Does anyone in the Bucker community know the purpose of the triangular marking on the CASA landing gear?  I have seen this marking in several pictures and can not figure out what it means.

Thanks. Brian