White gums and pain after root canal, what is this?

It's ok. When doing a root canal, your dentist places a clamp around your teeth, and sometimes this creates some gum pain for a few days after treatment. They also use some irrigation solutions that can cause the tissue to turn white. It is a temporary condition, and should soon resolve. If you have any questions, don't hesitate to call your dentist, and they can coach you more.
Not unusual. This may be related to having a rubber dam or trauma to the local area. You may experience some sloughing of the gum tissue over the next few days, however, should heal within a week or so.
Possible. The white gums and pain could be due to the irrigation solution that is used for the root canal or the clamp that is placed on the tooth to stabilize the rubber covering that is placed around the tooth.