In a large plastic bag, place cornish hens, lemon juice, and salt. Marinate for about 30 minutes, turning once.
Meanwhile, mix together yogurt, ginger, garlic, turmeric, and garam masala. Add food coloring, if using.
After lemon juice step is complete, transfer hens to a second plastic bag and pour yogurt sauce over the meat. Use your fingers to get marinade under the skin of the hens. Marinate for at least 3 hours or up to overnight for maximum flavor.
Bring hens to room temperature. Remove marinade from hens (as much as possible). Truss hens using twine.
Preheat oven to 500 degrees. Place hens on a rack over a large sheet pan. Bake for 20 minutes, then turn down heat to 400 degrees and bake for an additional 25-30 minutes or until internal temperature is 175 degrees and juices run clear.