I was once asked by a pupil what colour of flower she should wear in her button hole for her first public examination. As she was reading Physics and Philosophy, I thought a Do¨aut;ppler shift representation of the dynamic view of time would be most appropriate. Blue for the future, towards which we were travelling at a velocity of one second per second, red for the past from which we were receding equally quickly.

Other pupils reading Psychology and Philosophy interpreted it differently. Blue, they said, was right for going into an examination, because one felt blue about it: red was appropriate for the past, which one viewed through rose-tinted spectacles.

I now use colour-coded transparent folders for my papers:
blue for the distant future---lectures I am going to give next year
green for the near future---things I have got to deal with in the coming week
yellow for today red for things already done, but needing to be referred to again.