1. A method for converting input data representing a color formed from only two colors to output data representing a color formed from at least three colors, comprising the steps of: receiving the two-color input data in the form of two colors, a primary color and a secondary color; determining, for each color of the two-color input data, an equivalent color defined in a full color space by applying a first function to each color of the two-color input data; determining, from the two-color input data, a screen characteristic for the primary color and the secondary color; determining which screen characteristic is of a lesser value, and then determining if the lesser value is equal to zero; if the lesser value screen characteristic is zero, generating an intermediate output that is a function of only one of the primary and secondary colors, otherwise, generating an intermediate output that is a function of both the primary and secondary colors, wherein the intermediate outputs include a highlight color, a highlight color percentage and a black percentage; and processing the intermediate output using a second function to generate the output data representing a single color defined in at least three color space.