First I augment the tone of the photo a little to the yellow/brown color. This gives it a bit of the aged photos look, since these characters were from historical times.
Some photos I darken slightly to give it a somber look
Some photos I lighten to give it a a faded sun bleached look. Once again to give it the photo an aged look.
Than I boost the saturation just to make sure the coloUrs pop a little extra for that added artistic feel