If a tooth is dark yellow, can i brush it back white?

Probably not: If it's just a single tooth that is dark it is most likely dead. Usually this happens from trauma. See your dentist and let them know your concern. It may need a root canal and internal bleaching. A crown is usually placed over it and this will give you the color that matches the rest of your smile. Hope this helps :)

No: If all teeth have discolored see Dentist for professional cleaning followed by tooth whitening treatments. If only 1 tooth discolored it may be from previous trauma. If tooth is non-vital it will need root canal Rx and bleaching or a crown. If tooth is vital various bleaching or restorative techniques are available. If tooth has discolored from the inside, brushing the outside won't help.

Probably not: A tooth that is dark yellow most likely has a deep stain, is non-vital, or is naturally dark. These issues cannot be brushed away.