I am trying to cook mexican Nopales but they seem to loose their green look. Is there an ingredient that needs to be added or a special technique that would keep them as green as possible?
I am not familiar with nopales, but I would be astonished if their green color was determined by something else than chlorophyll. Chlorophyll is usually destroyed by normal cooking techniques. If you want to keep the color mostly green (some dulling is inevitable):