Paint brushes are used to add color to the leather. Many different sizes are used depending on the detail involved. I often use an extremely small brush for the nooks and crannies to make sure the color does not overflow into other partsof the design. Larger brushes are used to cover large areas with one color, or to apply a finishing coat of clear protectant.
Another coloring tool is the felt dauber which is used to cover large areas of leather with dye or finish.