As their name implies, the term 'Rainbow Face' derives from the yellow, red-orange and blue upper halves of the dinosaurs' bills. Barring their colorful faces, the Rainbow Faces are not very spectacular in appearance, primarily being green, with blue stripes and pale underbellies.
Their scelera colors and body colors vary from gender to gender, with males being a dark green with yellow scelera, and females being pale green with pink scelera.
Two individuals 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. 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.
The identity of the two Rainbow Faces from The Stone of Cold Fire remains ambiguous; because of their knowledge and means of departure, the most commonly accepted explanation for their existence is that they were extraterrestrials who had taken on saurian form in order to interact with the natives.
Various background, possibly non-alien Rainbow Faces appear in The Land Before Time IX: Journey to Big Water, The Land Before Time X: The Great Longneck Migration, and The Land Before Time XI: Invasion of the Tinysauruses.