Originally Posted by jeanericuser
In addition that effect happens when they are merged with an animal that helps regulate their sage energy. Jiraiya had ma and pa toad on his shoulders to allow him to access full sage power. Kabuto had several snakes that helped to manage his. Naruto since he can't do that he can only partially transform hence why his features are limited to frog eyes and discolorations on his face. The same I suspect is also true for orochimaru.
Actually, this is false. Jiraiya's appearance when he entered Sage mode is he never got the chakra balance perfect, so he entered an Imperfect Sage mode. Naruto's eyes transforming alone was a sign that he had the chakra balance perfect.
Jiraiya fusing with Ma and Pa was only so that he could keep using Sage mode by having them draw in the sage chakra while he had to move. Naruto got around the inability to do that by using his shadow clones.