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 'TrialList' List object, and all the possible stimulus colors are listed under it.
To get a full crossing of stimuli/colors, you can use a nested List within the TrialList to hold the 'StimColor' attribute. The selection of the nested 'ColorList' object should be set to 'Random', so that on each trial, the ForeColor property is randomly resolved with one of the values contained within ColorList.
In the Stroop experiment, a 'color' word (e.g., 'Green', 'Red', 'Blue') 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.