Requirements on color image fusion for situation awareness and target detection tasks were analyzed based on the characteristics of human visual system. Then a night vision fusion method was presented to improve target detectability by enhancing color contrast between the target and the background. The proposed fusion method relates hot and cold targets to the colors of intense red and cyan, respectively. According to the characteristics of infrared images, a color contrast enhancement ratio related to the divergence of the intensity of each pixel from the mean intensity of the infrared image was utilized to enhance color contrast between the target and the background. The enhancing method offsets the disadvantage of color transfer method in color contrast and improves target detectability. Experimental results demonstrate that the method can not only pop out both hot and cold targets, but also keep details of the background well. The situation awareness and target detectability can be improved by the method.