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?

Red is a great. I hope that it would be like the reaction videos of kids having their Cochlear implant turned on for the first time.

I'm not attempting to speculate, I'm just saying I wonder what the subjective experience would be like. I stopped trying to think what it would like to be a bat a while ago.

I think most people misunderstand color blindness in that most red-green colorblind can see red, it's just muted. I know what red looks like, but it needs to be plain old bright red.

protanopia: can't see red. protanomly: some red is visible.

The guy I worked with who was RG CB couldn't wire up stepper motors (typically use 4 wires, red green blue black), he couldn't tell the difference and had to use a multimeter.

Small tangent, but I first learned of the "What is it like to be a bat?" question via the book The Mountain in the Sea by Ray Nayler. Really good book that deals with the ethical problems of emerging sentience in a species of octopus, while set to the backdrop of climate change, sentient AI and overfished oceans.