Skin discoloration can be due to changes in melanin. Melanin is a skin pigment that gives color to the skin. Changes in melanin can also cause skin to be patchy. Treatment for skin discoloration includes using topical treatments.
Winglets increase an aircraft's operating efficiency by reducing what is called induced drag at the tips of the wings. An aircraft's wing is shaped to generate negative pressure on the upper surface and positive pressure on the lower surface as the aircraft moves forward.
On standard winglets we get something called interference drag. This is caused when air flows over sharp angles or curves. Imagine now cutting a knife through butter and how little force is required. This is because a knife is streamlined like the shape in the image below.