Pretty unusual to have half the class colour blind, OK there were only 6 of us but even so 3 colour blinders in one class isn't an every day occurence. Of course we entertained the others with our party trick of not being able to see the numbers, they thought it would be even more entertaining if they showed us some colour blind test of a more adult nature. Took me a while to work out what was so funnny as I tried to trace the outline of an indistinct line on the image. Try the non rude colourblind test on the Activity: Light waves.