Triversi

From BoardGameGeek:

Triversi is a three-player version of Reversi (Tri-riversi). Similar to the traditional two-player Reversi, you flip the opponent's pieces by sandwiching them with your own color pieces. However, unlike the traditional Reversi with black and white pieces, this version uses red, blue, and yellow pieces. This introduces the thrill of not always gaining points when flipping pieces. Players have the option to place a piece face-down. It is a strategic abstract game. -description from the publisher