In this test, you select a color from the drop-down menu, and press "Start" ... As soon as the background becomes that color, you must press "Stop" ... That time it takes between the appearence of the color, and your click, is called your Reaction Time. Waiting and not knowing is part of the test. So remember now, click "Start" place your cursor over the "Stop" button, and wait until you see the the page turn the color you selected. then and only then should you click "Stop" - got it? ... Enjoy.
Btw, some of these colors can take up to 20 seconds; give it time.Return to the ... Directory ... aka "Navigator."