I suppose it is possible. I've not seen a yellow lettering example of this early style triangle. The green was worn by both genders, there was no colored lettering to seperate male from female. The traditions stripe for the green Landjahr is the same color also for both genders like the lettering. I don't have the regulations for the earlier triangle to reference from, if there were even regualtions for it. The black Landjahr triangle did exist, that I am confident of. I had a discussion with Jeff Hammond regarding unusual triangles once and this is what he wrote me about the black Landjahr triangle.
"Thank you for sending the image of that quite unusual youth triangle. My initial reaction is that such a thing probably is not original, but I applied that test to one shoulder triangle and later found out that I missed out on an extremely rare triangle. One of my collector friends had gotten a Landjahr triangle (the typical green type), and he found that it had been sewn on top of a black Landjahr triangle. I bought the black triangle from him, but when I looked at it, I thought that it just couldn’t be right. For one thing the style of the lettering was different. I sent it back and got my money back. Well many years later I found out that the back Landjahr triangles with a different style of lettering were used for a short time. So that’s what I get for being overly skeptical. I missed out on an original triangle of a type that I will probably never see again."