Reddit mentions of Tiffen 52mm 30 Magenta Filter

>There is no specific wavelength for magenta so it isn't a colour. There have to be specific rules in science for what is a colour and what isn't.

I disagree. "Colour" is a perceptual phenomenon, under the realm of neurology and psychology, and the borders are largely determined by culture & language. Hungarians have 2 main words for what English speakers call reds, Russians have 2 words for blues, but Chinese & Japanese have a single character to cover blues & greens. So magenta is a valid color name if your culture says it is. That doesn't mean it must have a rigid formal definition.

Physical science (astronomy, physics, chemistry) has a better system than color names: specify a wavelength or frequency, or the interference pattern of multiple waves (accounting for phase). There's no confusion via cultural differences if you stick to that.

>Try and make a magenta filter

You can combine 2 filters for the appropriate wavelengths of red & blue, or you can just buy one.