1. A method for managing display colors of a three-dimensional virtual model, said method comprising: an entry step to enter a three-dimensional virtual model made up of a plurality of components; an attribute definition step to create an attribute list which defines a plurality of different attributes for components of said three-dimensional virtual model; a rule definition step to define a conversion rule for converting an attribute value into a display color for each attribute of said component; an attribute selection step to select an attribute to be color coded from said attribute list; a rule selection step to select a conversion rule corresponding to said selected attribute; and a display step to color-code display components of said three-dimensional virtual model in conformity with said selected conversion rule.