Black spot on top of veneer?

Most likely there is leakage under the veneer and the black spot you see is due to bacterial growth. Another possible cause, is a cavity under the veneer. I would recommend seeing your dentist to determine the cause of the black spot and have the veneer replaced if necessary. I hope this helps.  Follow me for more questions and answers.

its due to leakage . and black colour is because of bacterial growth between veneer and tooth surface. only option is replacement of that veneer.

Most likely, there is leakage under the
veneer, bacterial growth and stain. Since I have no idea about your homecare,
it is difficult to attribute the inflammation and bleeding in your gums to a
specific cause. I would guess, however,
that it is bacteria around the margins of the veneers. I recommend that you return to your dentist
to seek a solution. I feel certain that
the black spot, if it is under the veneer, needs to be corrected by replacing
the veneer.

A black spot under your veneer can be two things. The first is that it could be decay under the veneer. The second is called micro-leakage. This is bacteria getting under the veneer  and growing, causing the black color. Neither one is good. I would suggest calling your dentist for an appointment.