Human performance on color discrimination in visual display terminals may be affected by illuminant colors, the level of ambient illumination and background colors of the monitor. Few studies have focused on this topic. This study investigated human color discrimination ability in a simulated control room. Ten subjects were recruited as participants to perform a series of experimental tasks. A complete factorial (2 × 3 × 3) within-subject design was used. The independent variables were three illuminant colors (red, blue, and white), two ambient illumination levels (50 lux and 300 lux), and three background colors (black, blue and brown); the three dependent variables were the color discrimination ability (error scores), completion time and subject preference. The results showed that the illuminant colors and the screen background colors both significantly influenced human color discrimination ability (p<0.01). The result of this research can be used in control room design when considering the effect of color.