Printing small type in more than one color can be a nightmare for some printers. Keeping the type in register throughout the run is challenging and for you, this means fuzzy type that looks bad.
You can minimize this risk in the following way. Whenever possible, print small type in one color. Failing that, print the type in two colors, but make one of them a very light color. An example of this would be a color made up of 100 percent magenta and 100 percent yellow. If the yellow is out of register, only a trained eye with a loupe will see it.
You can also minimize problems by setting small type in a sans serif face. Helvetica Bold type, for instance, set even at 7 pt. in 100 percent magenta and 100 percent yellow will be clearer than Garamond set at the same size in the same colors because of the absence of serifs and thin stems. As a rule, avoid setting multi-colored type smaller than 10 pt.
If you have the budget and are already printing on a five or six unit press, consider printing the small type, rules, and reverse type (and any other elements) in a PMS color rather than a process color build. Keep in mind that this can add significantly to the final cost if it requires your printing on a larger, more complex press.