Complexion refers to the color of a person's skin, especially the face. If you have light skin, for example, you might be said to have a fair or pale complexion.
The general character of something can also be called its complexion. If your team's star quarterback is out with an injury, it will change the complexion of the next game and possibly the entire season. Complexion originally referred to the humors that in ancient Greek and Roman medicine supposedly made up a person's temperament and health. The word came from the Latin complexionem, or "combination," but as humorism fell out of favor, this definition of complexion also became obsolete.