Rainbow Face is the Land Before Time name for the dinosaur Gallimimus. They are called this because their bills are colored yellow, red-orange and blue. Two appear with rather major roles in The Land Before Time VII: The Stone of Cold Fire, one male and the other female.
It is these two who plant the rumor of the "Stone of Cold Fire"'s magical powers, which are proven a fabrication. They also tell the dinosaurs about "Beyond the Mysterious Beyond", but are not trying to reveal too much, as seen when the male occasionally almost reveals more than he should but is stopped by the female. Their motive seems to have been the broadening of saurian minds, with whose narrowness they had grown frustrated. At the end of the film, after they talk to Littlefoot, they disappear when they are suddenly surrounded by a shimmering pillar of light. When the light fades away, they are gone, whereupon Littlefoot looks into the sky and watches a bright light in the sky fly upward towards the stars. Two Rainbow Faces also appear in The Land Before Time X: The Great Longneck Migration with a Ouranosaurus and a Styracosaurus. Mo looks so colorful but he's not an Rainbow Face.
The identity of the Rainbow Faces remains ambiguous; because of their knowledge and means of departure, the most popular suggestion is that they were extraterrestrials who had taken on saurian form in order to interact with the natives. It is also unknown what relation the pair have.