If you possess a purely logical mind, then the appearance of your dice don't matter. Since all RPG dice roll pretty similarly and all are close enough to random for tabletop gaming purposes, then cheap dice are the only logical choice. This page lists all the cheapest dice available.
Almost all cheap dice are solid opaque colors. The reason for this is there is less waste in the manufacturing process. The manufacturer just tosses in a bunch of one kind of coloring (the plastic they start with is actually clear) and every set comes out looking the same. Since small air bubbles won't be visible, they can cool the dice faster, allowing them to produce more sets per hour, and they don't have any cast-offs common with multi-colored dice when the color mix doesn't work out right. But for the cost conscious, opaque colors provide a cheap dice set option that lets you get your dice for less, or spend just as much and get a lot more dice!