DARK AS MIDNIGHT: An athlete showing off his blackened tongue is the closing shot in the first spot for Quaker Oats Co.'s Gatorade Midnight Thunder. The new, blackberry-flavor addition to the line is opaque black in color (AA, Jan. 26). Blair Hayes of production company Sticks & Stones, New York, directed the commercial created by Foote, Cone & Belding, Chicago. Copywriter: Marisa Brown. Art director: Jim Bohan.