[lxdude]

Why not have 3 pinholes very close to each other (optimized in all respects for each color) - L and R (top/bottom whatever) reflected 90deg away from the centre which is left unaffected ...

Parallax issues could be smaller than the effects of the pinhole size/wavelength issues ?

Let's see...

Hole size could be optimized for each color.
It would require much shorter exposures, be easier to make, would be cheaper and easier to source materials with no need to acquire 1/3 reflectance pellicles.

Hmmm... I'm likin' it.