Whisk together the soy sauce, sugar, 2 teaspoons potato starch, sesame oil, and black pepper in a large bowl. Mix the pork into the marinade and turn until all the pork is covered. Allow to rest for 15 minutes.
To make the sauce, whisk together the water, vinegar, ketchup, 1/4 cup sugar, salt, 2 teaspoons potato starch, and red food coloring in a separate bowl. Set aside.
Dip the pork pieces in the beaten egg, then dredge in the 1 cup potato starch. Use your hand to press the starch onto the pork, assuring a consistent coating.
Heat the peanut oil in a wok over medium-high heat to a temperature of 375 degrees F (190 degrees C).
Fry the pork pieces in the hot oil until crisp and light brown, 4 to 5 minutes. Remove the pork from the oil and drain, keeping the oil hot. Return the drained pork pieces to the hot oil for 30 seconds more. Remove and drain again. Pour off all but 1 tablespoon of oil from the wok.
Heat 1 tablespoon of reserved oil in the wok over medium heat. Cook the green bell pepper, cayenne pepper, pineapple, garlic, and green onion in the heated oil for about 5 minutes. Add the sauce and stir until it thickens. Stir in the pork and toss until the pork is coated with sauce. Remove from heat and serve.
