Yellow teeth can be a cause of a lot of different issues. Please talk to a dental professional who can help determine why you are experiencing discoloration. It can be anywhere from coffee stains or stains from smoking. You can also look into whitening options.
Thank you for your question.
Decay will typically be very white if enamel is demineralized. Once the enamel is penetrated and the underlying dentin is exposed a yellow color will be apparent. Decay will then turn brown as the dentin begins to be eaten away by the bacteria.
A yellow coloration can be observed if you have limited enamel due to a developmental disorder, bulemia, or a diet high in acid.