That distinctive purple hue is a result of the IR filter. Filters on consumer cameras don't block 100% of IR, which is visible as that purple color. Useful for checking if remotes are working properly.
I don't think it's because of the IR filter. I have removed filters from several color webcams and they always see IR as purpley. I think it's the bayer filter - the different color channels clearly have different sensitivities to IR.
Yeah, what I mean is the existence, the visibility of a slight purple hue. If the camera has no IR filter, you don't just see a slight purple hue on the LED itself, but you see the light just like you'd see a visible wavelength LED.
I actually was obsessed with IR cameras and mods for some reason around 10-12 years ago. I remember using developed empty photo films to block visible light and let only IR through after removing the IR filter.
If you look at a quantum efficiency chart you will find that CMOS sensors are actually sensitive to 850nm IR light almost identically at all photosites regardless of the colour filter and then they gradually decline together as the wavelength increases. The colour cast is mostly due to the tuning and white balance of the image.
