If colors are only functional implementations in the brain doesn't that mean that there could be other colors than the one known to us by experience ( other than the ones from the light spectrum ) ?
If, then yes, although maybe we've reached some limit since our range of colours is already impressive.
To a person seeing things in black and white it would be easy for normally sighted people to prove there are other colours. So, somebody seeing more colours than we normally do may be able to offer us some indication that s/he does.
We are also supposed to perceive electromagnetic wavelengths slightly differently from each other, so there you are.
We may further conjecture that colours are coded in our brains through specific neurons or neuron structures, if so it seems reasonable that we could one day extend our range of colours, for example to be able to see objects in infrared light.
Would such colour feel similar to the original range of colours? It difficult to say. Reds, blues and yellows sort of feel different from black and white, or even greys. But if a new colour felt like a sound that would be counterproductive.
Maybe it could feel completely differently from anything we normally experience. That would be an awesome moment.
Well, fat chance.