There are many possible reasons for the yellow color occurring. One is that the antibiotic might have stained the teeth. Or another is that there is an infection and that's causing the other teeth to decay. You should probably have that looked at by a Dentist and they can asses exactly what the issue is and let you know what the remedy would be.

If you have any other questions, of my dentists friend's sites is pretty comprehensive so you may want to look for other answers there, Dentist Atlanta .