Think of:
* A cow's coat: Often described as mottled black and white.
* Marble: A mottled stone with swirls and variations in color.
* Leaves in autumn: Can have a mottled appearance with yellows, oranges, and reds.
It can also be used to describe a surface with uneven or irregular coloration:
* A mottled complexion: A skin tone with patches of color or unevenness.
* A mottled wall: One with patches of paint or discoloration.
Essentially, "mottled" describes something that has an irregular, patchy, or spotted appearance.