Colored contacts are contact lenses that will change your eye color or give some special effect to it. Prescription color contacts simply mean that they will have corrective effects on your vision (if you are near-sighted or far-sighted) and (like the name says) you need to have a prescription from an eye doctor to get them. So if you already use either eye glasses or normal contact lenses and would like to try color contact lenses instead, then you need them to have the corrective effect on your vision. Obviously you need the corrective effect so that you can see properly. Notice though that if you have only used eye glasses and not contact lenses, then you should go see an eye doctor to see what kind of contact lenses are good for your eyes. There is also a non-prescription version where the contacts will not have any corrective effect and they are used just for cosmetic reasons. Even if you were to get non-prescription contacts, you should still go see an eye doctor to see what type of contact lenses are good for your eyes if you haven't used contacts before (it won't hurt to take the safe way with your eyes).

Most color contact shops offer the option to get either non-prescription or prescription contacts and the only difference between the two is the corrective effect, so they are completely same otherwise. If you want to get yourself a pair of theatrical contacts (which have some special effect or unnatural color or shape) then you can't most likely get any corrective effect to them because they can often bought only as non-prescription since they are meant to be used only for cosmetic reasons. You need to remember this if you, for example, were going to buy a pair of vampire contacts for the next Halloween or get those sharingan eyes for the next role-playing session.