It would be interesting to know what kind of quality control measures there are in latex manufacturing and how much variation can occur in individual 1"X2" rectangles of latex cut out of the same sheet. I suspect the mixture formula for any "lot" of latex material probably is much more important than the dye used in that lot. However, there is no doubt that some lots of latex material makes for better sounding turkey calls than other lots. How much of that might be caused by the dye in the mixture? I don't know.
I'm not sure there is any latex made that is manufactured strictly for use in turkey calls. I think we are basically taking a product that is made more other uses and applying it to our craft. As such, I think every lot of material we use is more or less a crapshoot as to how well it is going to perform in a turkey call.