I guess the person would have no associations with the pure color red. Non-colorblind people have a life full of memories where red is associated with blood, lipstick, flushed cheeks, race cars, etc. plus the associated feelings.

I'm guessing they only really get the full effect of the therapy after they've lived without colorblindness for a while and made those associations.

Do you think there's a fundamental difference between getting a new color receptor and training yourself to recognize/differentiate more of the colors you already have the receptors to distinguish?