You are walking along and a Vehicle pulls up along side of you and starts shooting Paint Balls at you.

Do you have the right to return fire (CCW Permit). provided its safe to do so. IE: clear shot, not one else or Vehicle in your line of fire. except where the shots are coming from.

I say you do, as a paint ball weapon is just as dangerous as a fire arm.

Short answer No. You would be using what is recognized as deadly force against what is accepted as non-deadly force.

What if you recognize it as a GUN but did not know it was a paintgun, and you feared for your life? Do they have to shoot first before you can defend yourself?

My response is out of a concern for you. It is probably not the answer you want, but it is one that you need to consider carefully. Florida indeed has a "stand your ground law," which as you know allows an individual who is in fear of his life to defend himself. Once you have done that, it will be up to the jury in both the legal and civil courts (when the family of the deceased sues you for "wrongful death") to decide if you as an experienced user of weapons can tell the difference between a real weapon and a paint gun.