The color reference slide is to calibrate the scanner so you know that the colors you get in the final image are true to the original. Film stock is irrelevant. Once calibrated, you can scan anything the scanner can handle (in this case a dedicated film scanner for 35 mm film prints and slides). Then you can adjust for projector bulb variations if you so desire. But I believe the intent is to archive the accurate colors from a technicolor print - the closest we are going to get to the O-neg.

Photographers often use something similar to get accurate color prints. But in the case of a projector ready film, that has already been done and the case before us is how to get those colors from film to digital.