When I did the Hollywood Farmers Market, I would get this question all day. "No, there's no coconut milk in it." "No, it's not green." I would usually answer, "It's actually brown and has the consistency like gravy!" Here's why.
Popular in all Japanese households, it was introduced by the British (while India was under British colonial rule) sometime during the late 1800s. Japanese military officials dealing with vitamin deficiencies among soldiers realized it was the lack of wheat in a mostly white rice diet. The way to get soldiers to consume more wheat was to thicken the sauce with a roux or a flour based thickening method. Of course served with rice.
Naturally, over time different regional varieties did emerge but the foundation of the sauce being curry powder and tomato base. And even within regions, there are household recipes. The one I make uses apples and lots of caramelized onions among other stuff (I can't tell you all my family secrets!). My mom would cook a giant pot and we would eat it for dinner. It would then sit on the stove over night (room temp) and then, "click!" back on for breakfast....and then repeat for lunch until the pot was all gone.
Being a professional, I probably shouldn't test the resilience of your stomachs to food sitting out at room temperature for days on end. Sure it won't be just like mom's recipe but it's pretty darn close. Come try the mama Hashi beef curry next month and see for yourself!