Abstract: Recently there has been an increase in awareness of work/life stressors and their debilitating affect on human functionality. These stressors can arise from environmental conditions, poor quality artificial lighting and/or too much or too little ambient lighting, poorly configured or ineffectual display screens. The invention includes a method of presenting an image to be viewed by the subject on a background of a first colour, and by way of an iterative process a user is led through a series of screens in order to determine their optimum colour combination. A means is provided for storing reaction times and for varying the image to be viewed in a second and subsequent interval, so as to derive second and subsequent reaction times. An optimum colour is selected that corresponds to the quickest reaction time.