Nothing. This is just to show the difference between colored lines and black (or dark colored) lines. As you can see colored lines make the color seem more vibrant in comparison. Although this specific comparison is a little unfair, considering the fact that only the colors of the hair, dress, and skin are the same between the two. the bow and bandage's shading are different color, and the hair tie and collar are the same color as the outline.
Art by me Character design by me.
