What would it look like? I mean, we see via light receptors in our eyes. Hell, every sensor we have is all about absorbing or reflecting various forms of radiation (light), so when we stop light altogether ... how do we know? What does it look like?
They know it's been stopped (paused, actually) because it hasn't struck the detector on the other side of the media. What does it look like? Nothing. Because unless the light is traveling and strikes your eye you cannot see it. (Note: this is NOT a visual experiment at all.)
A picture of stopped light.... http://www.seas.harvard.edu/haulab/slow_light_project/slow_light_project.htm
