1. Color deficiencies 8% of white U.S. males are red/green blind (less in other races; white females: 0.5%) these colors appear medium-gray *    Design for monochrome first, and add       color as a  redundant device.       If this is not (fully) possible, objects       should not only be distinguished       by their amount of red or green.

2. Adaptation problems

Colors have different wavelengths, ranging from red (610nm) to orange, yellow,
green, blue and violett (380nm). Pupils must refocus when colors change.

*    When users' eyes must constantly switch between objects of
      different color, avoid combinations of colors that differ strongly
      in their wavelengths (this hold particularly true for elderly users).