Black and white film blocks most of the IR spectrum, different colour stocks block from almost none to around 30% in various areas of the frequency.
Other manufacturers have had better results with Blue LEDs on the sprocket area, and placing them before the camera sensor so that there is no light bleed.
If you are going slow (1-3fps) almost any sensor will work, once you get up to speed it becomes a problem. It might be worth playing with polarisers to see what effect they have - anything that might magnify the difference between the clear stock and empty space is worth investigating. However remember that every stock type has different properties.
BTW, the Muller uses the same triggered light source for capturing that I have outlined in other posts designed by Frank Vine.