Instead of using flat colors to fill in the animations, we can use a certain texture.

1. We place the texture we want to use on a layer below the character to be textured. We will see the character over the actual texture.
2. Set the paint transparency value to 0. Select the fill tool and click inside the area where the texture should be placed. The area will become fully transparent and the character will appear textured.
3. Now, set the paint transparency value to 100% and fill in the outside of the character.
4. Merge the character and texture layers.
5. Set the transparency back to 0% and fill once again the outside of the character with this color, returning the area surrounding the character to its initial transparency.

Note: To achieve the effect that the texture goes along with the character, you will only need to setup the corresponding camera layer for the texture.