It is not uncommon for root canal teeth to become grey, black or bluish. Have a dentist confirm you do not have any decay under the filling in the back of the tooth where the root canal was done. You may have a leaking filling where decay has gotten into the tooth.if no decay, ask about a walking bleach. It may whiten enough so you are happy. The other option is a porcelain crown to block out the dark shade below.

It is not uncommon for teeth to become very dark after a root canal. My suggestion would be to have a permanent crown made. You do appear to be young and usually dentists prefer to be more conservative with younger people. In your situation I don't think any other restoration will block out the color.

After a tooth dies, which is why you required a root canal, a tooth often becomes discolored because it has no vitality to it anymore. In your case, your tooth needs to be examined to see if there is any recurrent decay and then would benefit from having a porcelain crown placed on it, which can be made a whiter shade to match your other teeth.