Have them put a porcelain crown on them, not a porcelain fused to metal or porcelain fused to gold. The results will be super looking and very, very natural looking. Today’s full porcelain crowns are very durable too.
If the tooth is darkened due to root canal or nerve damage you really need to do it. Nerve damage to a tooth removes it’s source of life and makes the tooth brittle, meaning one day you’ll break it. If it’s a darkness caused by age or by childhood tetracycline you won’t have the brittleness though.
Here’s the scoop: you’ll go in, they take an impression for your temporary, get numb, they’ll shape your tooth for the crown, take an impression for the lab, make your temporary, glue it in, send you home. In about two weeks you’ll come in, the temp will be removed and the crown will be permanently cemented in after bite is adjusted and proof that you are happy with the esthetics.