Step 1: Remove the membranes from the back of the ribs. Arrange the lamb ribs in a roasting pan.
Step 2: Roast the spices: In a dry skillet over medium heat roast the cumin seeds until fragrant and lightly browned, 30 seconds. Transfer to a bowl to cool. Roast the garam masala the same way. Grind the cumin seeds to a powder in a spice mill.
Step 3: Make the tandoori marinade: Place the cumin, garam masala, garlic, ginger, salt, cardamom, mace, cayenne, orange food coloring, if using, and nutmeg in a food processor and process to a coarse paste. Add the vinegar and process to a smooth paste. Add the yogurt, lemon juice, and mustard or canola oil and process just to blend.
Step 4: Using a spatula, spread the tandoori marinade over the ribs on both sides. Place the ribs in large resealable plastic bags, 2 racks to a bag. Spoon in any excess marinade. Marinate the ribs in the refrigerator overnight or for 24 hours, turning several times so they marinate evenly.
Step 5: The next day, set up your grill for indirect grilling and preheat to medium-high. Arrange the racks bone side down on the grate over the drip pan away from direct heat. Indirect grill the ribs until browned and cooked through, 30 to 40 minutes.
Step 6: Just before serving, brush the ribs on both sides with melted butter. Move directly over the fire and grill until sizzling and browned on both sides, 1 to 2 minutes per side.
Step 7: Transfer to a platter and serve at once with lemon wedges for squeezing and the herb chutney on the side.