If the vegetables are growing illuminated exclusively by blue light,
will they be different in taste from the vegetables which are growing
illuminated by, say, exclusively green light ? What would be the
taste ?

(I presume that the chlorofylle in the plants needs to be illuminated
by the light of a certain wavelength or above, in order for the
chemical reaction of photosynthesis to take place. This will probably
result in different taste molecules been formed. That's all I know...)