One Dark Front Tooth - Options?

It sounds as if you are on the right path, treating infection and pain.  Once complete, it is likely this tooth will need a full coverage crown if not a veneer.  The challenge for the dentist will be to match this tooth to the others, not just in color but in shape, contour and texture.

A consideration here would be to KöR whiten all of your teeth prior making the crown or veneer.  This would make it easier to match color AND brighten your smile.  Your dentist will likely need to use a material that is opaque enough to block the color of the darker tooth and still look natural.

Doing this well takes a talented and experienced cosmetic dentist, as not all dental offices are equipped to deliver aesthetic results to such challenges.

A veneers is a thin piece of porcelain that is translucent, so light passes through it. It is not a good option for masking a dark tooth.

You could try internally bleaching the tooth after the root canal is completed. There is a small risk of root resorption with this procedure.

The other option is to place a crown over the tooth to block out the dark color. 

My material of preference is a zirconia/porcelain crown.

Matching ONE front tooth is about the most difficult challenge a dentist faces, even one with much cosmetic experience.  If it's also dark from trauma, it's that much harder!  I would usually recommend bleaching everything first, seeing how light you can get that tooth, and then doing an all porcelain veneer or crown, depending on the amount of tooth structure remaining.  I usually try to avoid placing a post if there is sufficient tooth structure left, as they tend to weaken the teeth.  This link shows a patient post-trauma where one porcelain veneer was done on the dark tooth after bleaching.

In the modern world of technology, we have many options of getting the right shade.Digital shade matching gives us the ability to conquer the trickiest shade challenges all day, every day, instantly and accurately. Also the dentist can have the lab tech come in personally to get you the right shade for your discolored tooth.Since you are getting root canal treatment on that tooth, the most ideal option is to put a full coverage crown on that tooth. The reason being first and foremost the tooth is discolored and also after the root canal treatment the tooth itself is not very strong and full coverage will protect it from further breakdown. You could also do veneer but root canal treated teeth usually get darker as time passes and you might need to replace your restoration.

When a tooth is traumatized and the nerve damaged, the tooth may darken due to death of the nerve.  A root canal therapy is your only option.  Sometimes, an internal bleaching procedure can be done after root canal therapy to lighten the tooth.  When internal bleaching is not enough, a crown or porcelain veneer is indicated to mask the discoloration.  You indicated this was an upper central incisor, the focal point of the smile.  Under these circumstances, I would recommend doing the same procedure, crown or veneer, on both upper central incisors to provide an aesthetic match.