The idea behind Refractors (the cards) is that they reflect a light spectrum, as in, a rainbow of light. The best way to tell whether or not a card is a refractor is to hold it up to a light source and see if you can see a spectrum of colors. Regular Chrome cards will not reflect any sort of rainbow light, it should just reflect the light from the source.
Of course, actual refraction doesn't happen because the cards themselves are not transparent.
http://myweb.cwpost.liu.edu/vdivener/notes/prism_refract.gif
As usual, Topps makes things confusing by not being consistent with labeling refractors, sometimes releasing cards that are "refractors" but don't have a non-refractor version, and doing other rainbowy-type stuff with cards.