In this sample the color of the word is varied by setting the Stimulus object's ForeColor property to an attribute reference. The attribute is then created in the Trial List, and all the possible stimulus colors are listed under it.
To get a full crossing of stimuli/colors, you can use a nested List on the trial List to hold the Color attribute. The selection of the nested Color List should be set to Random, so that on each trial, the ForeColor property is randomly resolved with one of the values on the ColorList.
In the Stroop experiment, a color word (e.g., "Green", "Red" is displayed to the subject in varying colors. The color in which the word is written may or may not match the word itself. The subject is instructed to respond to one or the other -- the stimulus word OR the color of the displayed stimulus.