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 do.
It’s concerned with a vivid subjective experience of a ‘new’ colour, what I think philosophers would call qualia.
Qualia are hard to explain just from the physical facts. Knowing the wavelength of light may show that it is red but does not explain its redness, the experience we have. Robots can recognise red but that does not seem the same as us seeing its red quality.
The new colours that people can be induced to experience are reddish-green and bluish-yellow. Scientific American for January 2010 reported these experiments, which improve on ones done many years ago but not fully appreciated at the time.
At Indigo Thoughts you can see images that may let you see bluish-yellow and reddish-green. They work for me to an extent, although it’s hard to keep my eyes crossed, and as soon as I focus on the images the ‘new’ colour goes away.