I have a similar green parka... there are several things you can do with that shade of green. You don't have to go with black jeans, as indigo / dark jeans will work great too. You can throw in some shades of brown, perhaps some brown shoes, or even khaki chinos / jeans with black boots if you haven't got brown shoes but want something other than standard jeans. Dressing it up a bit isn't hard either; it might not be in the same league as a mac, but you can wear it with a shirt and tie underneath all the same.