While previous research has addressed air traffic controller workload as a function of cognitive complexity due to environmental and to a lesser degree, organizational factors, significantly less attention has been paid to the role of displays and complexity in the ATC environment. One drawback to new display technology is that in dynamic human supervisory control domains, it is not always clear whether a decision support interface actually alleviates or contributes to the problem of complexity. In an attempt to quantify the influence of environmental and display complexity factors on cognitive complexity, an experiment was conducted to determine if these two components could be effectively measured. Results revealed that the environmental factor of increasing aircraft number affected subject performance only slightly more than the display complexity factor of increased color categories. These findings are important because the use of color in displays is meant to reduce environmental complexity, not add to it.