1. An image generation apparatus comprising: an image-data generation unit that generates image data of an evaluation image having a first reference color, a second reference color, a first evaluation color, and a second evaluation color, the first reference color and the second reference color being determined using a relationship in which the first reference color and the second reference color are paired in a predetermined color space, the first evaluation color and the second evaluation color being colors between the first reference color and the second reference color in the predetermined color space, the first evaluation color being determined with respect to the first reference color, the second evaluation color being determined with respect to the second reference color and being different from the first evaluation color; an image-data output unit that outputs the image data to a display device that is caused to display the evaluation image; and a retaining unit that retains image data of the first evaluation color and image data of the second evaluation color obtained when an image having the first evaluation color looks the same as an image having the second evaluation color in terms of brightness or tint in a case where the evaluation image is displayed on the display device.