Dear Vika: some people are "stolid" meaning they show little emotion, but may not even be hiding any.
British upper class members pride themselves on being reserved and having a stiff upper lip, and feel superior to people who reveal their emothons. Yankees pride themselves on understatement, and in general are not comfortable with emotional displays. I know what you mean by an "open person" but perhaps some of our other members might have suggestions for improvement on that. At the moment I cannot think of one. Bill