Atreyu was supposed to be green.
The hero Atreyu was a member of the Green Skins tribe. But the movie directors decided that actor Noah Hathaway should keep his own color.
This is 1 of 15 facts about the 1984 children's movie The NeverEnding Story rounded up by BuzzFeed. They include how the Falkor puppet was operated and who now owns the Auryn medallion.
The movie The NeverEnding Story is based on Michael Ende's novel The Neverending Story. It's excellent and I highly recommend it, especially as the movie had to cut out a lot in order to fit into 107 minutes. I own a first US edition which is printed in red and green ink, alternating between the two worlds. The visual effect is particularly striking as Bastian is about to cross over into Fantasia.