An apparatus sets a chromaticity point serving as a gray reference in a color gamut of a color space that an output device is able to output, specifies, in the color gamut of the color space that the output device is able to output, a first minimum lightness point on a lightness axis of the set chromaticity point and a second minimum lightness point that is achromatic, and generates a gray line that passes through a black point that is a minimum lightness point on a line connecting the first minimum lightness point and the second minimum lightness point, the first minimum lightness point, and the set chromaticity point and reaches a white point in the color gamut of the color space that the output device is able to output.