The green is the fenugreek leaves. It did have a particularly distinctive smell but in the sauce, its flavor appears very subtle.
This is based on the recipe from Washington Post but has been modified.
Ingredients:
FOR THE CHICKEN
4 chicken thighs (trimmed of excess fat), cut into 1 1/2-inch chunks
fresh lime juice (from 2 limes)
1/8 tsp. cayenne pepper (or more to taste).
3/4 teaspoon sweet paprika
2 teaspoons garam masala (spice blend)
1 1/2 teaspoons kosher salt
1/4 cup plain, full-fat yogurt
2 cloves garlic minced
One 2-inch piece peeled fresh ginger root, minced (1 tablespoon)
FOR THE SAUCE
4 tablespoons (1/2 stick) unsalted butter
15 ounces canned plain tomato sauce
1/4 cup dried fenugreek leaves, soaked in a bowl of water for 15 minutes and skimmed off the top.
1/8 teaspoon ground cayenne pepper.
1 1/2 teaspoons sugar
3/4 teaspoon kosher salt
1/2 cup heavy cream (we used much less)
1 teaspoon ground cumin
Directions:
1. For the chicken: Combine the chicken pieces with the lime juice, cayenne pepper, paprika, garam masala, salt, yogurt, garlic and ginger in a mixing bowl until evenly coated. Cover and marinate in the refrigerator for at least 30 minutes, and up to overnight.
2. Take the chicken pieces out of the marinade and put into a frying pan with some peanut oil (there will still be marinade on the pieces). Cook stirring occasionally until the pieces are tender. Remove the chicken from the liquid that forms in the pan and discard the liquid.
3. In a clean frying pan melt 3 tablespoons of the butter over medium heat. As soon as it melts (without browning), pour in the tomato sauce. Stir in the fenugreek leaves, cayenne pepper, sugar and salt. Increase the heat to medium-high; cook just long enough so the sauce begins to bubble. Reduce the heat to medium-low, partially cover and cook for 12 to 15 minutes, stirring occasionally.
4. Put the chicken pieces into the sauce, along with any accumulated juices. Stir in the cream and cumin, then cover and cook for 6 to 8 minutes, stirring occasionally, so the chicken absorbs some of the rich flavors in the sauce.
5. Uncover the pan and add the remaining tablespoon of butter; once it has melted, stir it into the sauce. Serve right away.
Although my wife cut the cayenne pepper in half from what was specified in the original recipe, it was still plenty spicy for us. She added some yogurt to "turn down" the heat in her serving but for me, it was just right amount of heat without yogurt. We are not entirely sure the fenugreek really added any particular flavor but this was a good curry dish. The chicken was very tender and flavorful due to the marinade.