Hi. Welcome to Healthcaremagic. I read your query. As you mentioned having a yellow spot on gums after having gingivectomy and veeners, have you noticed any discharge ever? If so, you need to consult your dentist for infection. It can also be the part of normal healing process, so wait and watch for 1-2 weeks. Maintain oral hygiene. If the spot persists, then it is the discolouration of gum due to chemicals used during veenering. It can be removed easily by laser diode in single sitting. Consult your oral surgeon for this. Hope the answer helps you. Thank you!