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 regardle

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.