First, a disclaimer: In no way does this recipe claim to be an authentic interpretation of Kashmiri rogan josh, hence the title, "Not Your Amma's (common Indian term for grandma) Rogan Josh."
"Real" rogan josh comes from the Kashmir region of India, where they have Kashmir chilies (mirch/i). These chilies give the dish its signature red color, but are not necessarily easy to procure in their whole form. Ground kashmir chilli powder can be found in certain Desi groceries, however, "real" rogan josh is supposed to have the dried whole mirchi. Paprika is also a common substitute in Indian restaurants due to its color and mild flavor.