Funny you should mention purple. The brand I advertise, we use (92, 45, 145) as our brand color. Wow, what a pain for daylight balanced, RGB.
It helps to shoot in tungsten balanced–as you mentioned–not anything else. Why you ask? Well, there’s a long seminar worth watching on panavision’s Web site on all things digital imaging, part of which is how white balance works. Here’s that link: https://media.panavision.com/ScreeningRoom/Screening_Room/Demystifying_Part1.html
As I remember it (always a suspect problem, my memory so please check for yourself) is, basically, when you shoot in day light, you have to “remove” blue from the picture, which is done by clipping the blue signal before it even gets digitized. In other words, purple is a “pita” because there isn’t enough blue in your signal, the hardware, the electronics, to mix with the relative amounts of Red and Green (and of course, there is more green in the signal). Tungsten will render purple because tungsten is normally when all RGB levels are equal.
You might want to experiment with other white balance “fixes.” What will happen if you use a yellow filter and white balance? In order to compensate, will an extra amount of blue photons be yanked through the yellow?