Thanks Bob and Jean-David for your real life examples requiring top notch colour acuity. Jean-David, was it impractical to have the (chips from the) Munsell<http://en.wikipedia.org/wiki/Munsell_color_system>Book of Color on hand when studying the picture coding for digital TV transmissions. Fancy having to memorise 4000 different colour chips ! rgds Peter 2009/11/10 Jean-David Beyer <jeandavid8@xxxxxxxxxxx> > It took me and my fellow trained observers several months to learn the 4000 > or so > color chips in the Munsell Book of Color. And we were retested about > once a week, IIRC. >