People have already been cured of complete blindness from birth (e.g. http://www.newyorker.com/tech/elements/people-cured-blindness-see ). Not much seems to be revealed by this, especially since in the Mary's room experiment, she is supposed to know everything there is to know about color in advance, and obviously this is not true in such cases.
It seems possible that soon there may be a cure for colourblindness. The Mary's Room thought experiment attempts to pin down something about the nature of qualia in a contrived but similar situation, but my feeling is that the actual result of such an experiment would not be obvious. Would we consider the experiment valid if it was performed on somebody familiar with blue and green, but not red?