Um, I know some early chemical solutions were used to make some horns two tone, with a blackened tip and very light colored body.
Which is odd that folks doing living history would wear a horn made sometime within a 50 year period and contemporary to their persona..., and then age it to look like it's 200 years old...., a really BAD reenactorism....
I doubt it. The primary cattle that the horn would've been made of would've likely been English Red Cattle, and they don't always have white portion of their horns. Nobody today, though, is making utility horns when it comes to horn making. The reason why I bought a dyed-brown horn for hunting, was because of the yahoos out there in public areas adjacent to where I hunt or when I'm in public hunting areas, and they have modern optics and will take a pot-shot at a bit of white moving through the woods.
Back in the day of the powder horn, the white horn was for embellishment purposes, and likely not the norm as mentioned the most common cattle didn't always have the necessary color horns. The lack of a coloring would also not have given the hunter away to the deer. I've stood completely still in the woods during summer scouting, wearing bright colors, and the deer took no notice of me. The use of hunter orange would also spook deer if that was the case. The white area of the horn is a LOT smaller than the area of blaze orange required in all states, and while a deer's eyesight does not see orange, blaze orange looks like white to the deer. The hunter would have a lot more problems with his movement, like his swinging arms, or his face, than the color of the horn