Are my crowns too short & how to mask dark tooth under crown? (Photo)

I knocked both front teeth out when I was younger and had root canals performed. 20 years later I finally had my crowns redone to look better. One tooth is dark and it is showing through. So far, they look great in bright natural light but the one tooth looks dark in dim lighting or inside lighting. Is there a way to cover the darkness of the tooth before the crown goes on to mask it? Also, are these too short?