Heat ghee in large pan. Add onion, capsicum, garlic, ginger and ground spice; cook, stirring, until onions are browned lightly. Add tomato paste, crushed tomatoes, chicken fillets and chicken stock; simmer covered until chicken is cooked through. Stir in cream, tamarind and food colouring, if using. Simmer; uncovered about 15 minutes or until mixture has thickened slightly.