There are a surprising number of green chillies. Certain varieties, are picked when they go green before heading onto red, sometimes purple, but almost always very hot. Look out for an Asian grocer's shop that has glorious Bangladeshi chillies: green, about 2-3 inches and slightly curved. When making Indian food or Thai, I'll throw in about 4 or 5, but without the faff of removing the seeds. I like mine hot.
Scotch Bonnets are something else. Be very careful with those lil’ piggies, they’re evil.