Is that true though? How would Mary know that the banana is blue and not yellow, unless she is TOLD that the banana is blue? Or that she can compare it with items that she can see that are labeled "yellow" and are actually yellow vs items that are labelled "blue" and actually blue?

Knowing all the physical theory behind colour perception, wavelengths etc doesn't mean that she suddenly has the ability to measure wavelengths with her eyes having never seen colour before.

Jackson's argument still stands.