Fluorescent colors are fluorescent because they literally glow – in real life that is. What makes them appear fluorescent is actually that they absorb UV light that the human eye cannot see. They then release this UV light as a form of energy that puts off visible light.
Used to be, in the early stages of fluorescent dyes and paints, that this would only be visible with the use of a black light. When the black light shone, the UV reflected light showed up.