This is an example of the Pop-Out Phenomenon. This phenomenon happens when facing a visual stimulus consisting of many similar looking items but there is just one which clearly stands out from the rest. This is exactly what happens which the suspects. All are white but one black, who visually stands out from the rest.
Instead, the Cocktail Party Effect is related to auditory attention, blindsight is related to responses of blind people when facing certain types of stimulus, and finally, dual processing refers to the origin of thoughts in the brain.