In a large bowl, combine yogurt, cornstarch,ginger garlic paste,chile powder,lemon juice, food colour & salt. Mix well.The marinade will look pink now which will turn into a luscious red when the chicken is fried. Add the chicken pieces and mix to combine. If you have the time, let it marinate in the fridge for 20 minutes.
Heat about 2 cups of oil in a deep saucepan. When the oil is hot but not smoking, add a few pieces of chicken and fry till they are crisp on the outside and cooked on the inside, 2-3 minutes Remove the pieces using a slotted spoon and drain on a paper towel. Continue until you are done with all the pieces.
Place chicken on a serving platter.
In a small pan/skillet, heat 2 tbsp oil and when it begins to shimmer, add the mustard seeds. When the seeds begin to sizzle, add the green chilies & curry leaves. Fry for about 30 secs. If you want you can add about 1/4 tsp more of red chilie powder to the oil just before removing it from heat.
Pour over the chicken and serve.