What is the cause of my yellow teeth?

hi there, when i was 12 i slipped on a floor and snaped my to front teeth in half, i had 2 root cs and now i am 18 iv been back and they said that the roor cs wernt sucsesfull so i need an operation to remove the infection on both fron teeth, ever since i fell my teeth have been yellow any know what that could be ?? thanks 4 lookin