I wouldn't make a guest bedroom to nice than people will never leave (this I know from experience). Dark colors are great but you are going to need a lot of light in the room so the inhabitants can see.

I really like SW Oceanside (was their 2018 color of the year) and BM Galapagos Turquoise. Bedrooms can handle darker colors IMO, just make sure you have adequate lighting so that if someone needs it brighter it can happen.

I think one dark tone guest room is enough for one house.

BM Naples Blue 2057-30

IMo bedroom colors are decided from the bedding so show that and it will help with deciding wall colors I prefer a much more subtle bedroom for guests that is restful.

SW 7620 Seaworthy

I know this is old but what did you end up using? Can you send pics as I am looking for the perfect Teal as well. Thanks

Ben Moore Twilight 2058-10 is a great color, very dark and moody, it's a chameleon color. Depending on time of day / lighting, sometimes looks blue, sometimes greenish, and almost black in low lighting.