There are a couple of options a new porcelain crown made instructing the lab that the tooth is black underneath and an opaque liner can be made as part of the crown to mask the colour from coming through. The other options are keep the existing crown open a small access through the back into the tooth and do an internal whitening/bleaching to lighten the tooth. Or do internal whitening and replace crown. Seeing as the crown is only a couple of years old discuss with the dentist who placed it. Obviously I do not know what you were told re the limitations of an all porcelain crown over a dark tooth before you went ahead.
Porcelain veneers would close the gap but your teeth would end up looking too wide which would look very odd. Usually the best way forward would be to have braces to close the gap. Sometimes veneers can be done but would often need your 6 front teeth doing and make all of them slightly wider so the 2 middle ones don't end up too wide.
