Researchers have revived an idea and a question that has been asked before, probably many times.
Can we see new colours?
For example Terry Pratchett's first DiscWorld introduced an eighth rainbow colour octarine, a 'fluorescent greenish-yellow-purple'.
It seems the answer is yes!
The question is not whether our eyes might somehow respond to ultra-violet, like a bee's, or have more types of colour receptor, like some fishes have.
It's concerned with a vivid subjective experience of a 'new' colour, what I think philosophers would call qualia. Qualia are hard to derive just as a consequence of the objective facts (thus knowing the wavelength of light may show that it is red but does not explain its redness, the experience).
The new colours that people can be induced to experience are reddish-green and bluish-yellow. Scientific American for January 2010 reports these experiments, which improve on ones done many years ago but not fully appreciated at the time.
But all the same these experiences are dependent on the physical properies of the brain, it seems. So are they true qualia?
I have a great respect for the man that stood foward claiming he was 'not quite right'
I can answer your question from a personal perspective and with some experiece with the spectroiscope at SMXR358 last summer, migh be able to clear up a few queries.
I, as many people, can resolve seven distinguishable colours:
Red, Orange, Yellow, Green, Blue-Green (Cyan), Blue and Violet (400nm). Actually, at 45, I can see slightly shorter wavelengths down to about 370nm but they still look violet, only dimmer. If there were an eigth it would be yellow green (yuk).
Loving Awareness? Try it, You'll like it!