• Do not use more than 4-7 colors per screen
• Color impression varies, depending on the background

              A possible color model

• To distinguish small objects, they should not only differ in their colors but also in their lightness (= amount of achromatic color, ranging from white over grey to black)   aa   aa
• For very fine details, use black and white.
• To draw attention to an object, make it differ from its environment in terms of its brightness and saturation (brightness is determined by the intensity of the light source; a saturated color is one that is composed of light with a narrow spectrum)
  E xample:          

  a

  a

  a

  a

  Green letter against green background that is distinguished in (a) nothing, (b) lightness (not brightness!), (c) saturation, (d) lightness and saturation.

Reading becomes harder if colors differ both in saturation and in their spectra.