In the forest kingdom, there are sheep roaming around that you can shear. Once you build a paint shop, you are able to paint them by dropping a painter on them. However, you cannot reach the last 2 sheep until you can build bridges, as the last 2 sheep are on an island in the bottom right of the map. Once you have the bridges in place, paint all of them and it will pop.
(You should probably paint all of the mainland sheep as soon as you get the painter, because it's easier to find them when there are fewer buildings. Also, if you exit the game, it might make the sheep white again, but they have still been painted. You will still only need to do the last 2 island sheep.)