If your house is "dark" then you should definitely go with a lighter colored paint. It doesn't necessarily have to be plain white but something with lots of white in it would brighten up the space! Also selecting lighter colors for big furniture and area rugs will help. :)

I agree about the light colored walls for a home with very little natural lighting. Also placing a large mirror somewhere to reflect the light that does exist in the room can be helpful.

We are looking for a light color (maybe soft white or gray) to compliment halcyon green. May I ask what you used or any other recommendations?

All these are higher chroma neutrals that compliment SW Halcyon Green and the the higher chroma would cut-through the dim light.

BM OC-6 Feather Down

BM OC-35 Spanish White

SW 7568 Neutral Ground