Dark tooth still showing after porcelain crown.

I had a root canal way back. Years after, my tooth started to darken, particularly near the gumline. My dentist suggested a veneer. It didn't cover it all thoug it lessened a bit. It kept bothering me so I finally opted for an all porcelain crown. Now, its still dark and seems to cast a shadow over the whole tooth. What other options do I have? Is this because the root canal was done poorly?