First, it is important to understand that in Florida the negligence laws include comparative fault. Under comparative fault laws, a jury can apportion fault between all parties (and even non-parties) to the lawsuit.
If there is proof that a car ran a red light, that would certainly suggest that that car is at fault and likely bears most of the fault. However, that person may argue that the other vehicle (that had the green light) fault bears some fault. The argument would be that the car could have avoided the accident, had they taken some precautionary measure. Depending upon how the accident happened would give us some idea of whether this would be a strong or weak defense.
For example, if the car that ran the red light was hit by the other car towards to rear side of the car, then the argument would be that the car that ran the red light almost made it and thus the other car had time to veer out of the way and avoid the accident. Of course, it would be up to a jury to determine the fault between the parties and they could do whatever they saw fit, based on the evidence. On the other hand, if the car that ran the red light hit the side of the other car, then this same argument would be much, much weaker.