How many times can a Dental Crown be replaced?

I read that every time you get a new dental crown they have to destroy a little more of your tooth. So how many times approximately can one get his crown replaced before another crown will be out of the option? Also, I have one front tooth that turned grey due to root canal, I heard getting a dental crown on one front tooth is nearly impossible for a good match. So what are my best options to fix my dark front tooth and get matching teeth? (Half the tooth was chipped and is now "pasted" back on)