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.
AOA is one of the most important parameters for understanding airplane performance and handling (see What Is Angle of Attack?) because a typical wing has a limited range of angles of attack over which it can function efficiently. In its simplest form, lift is a function of speed, air density, wing area, and AOA.