A method of coloring a target image includes generating at least one target mask including a part of the target image by using a first artificial neural network, which has been trained; generating at least one reference mask that corresponds to the at least one target mask and includes at least part of a reference image, by using the first artificial neural network; generating at least one colored target mask by coloring the at least one target mask in reference to the color of the at least one reference mask; and generating a colored target image from the target image, the at least one target mask, and the at least one colored target mask by using a second artificial neural network, which has been trained.