An acceptable luminance levels of a character color and a back-ground color were adjusted by twenty six subjects. A preferable color-on-color combinations were estimated by method of pair comparisons. Visual fatigue was measured after prolonged VDT work with a positive and negative presentation mode of VDT screen. The results show that the acceptable luminance value is about 30 cd/m^2,a dark-background VDT are prefered to a light-background VDT, and a lesser degree of visual fatigue is induced with the positive presentation mode.