Maybe, but I figured it fit because it's related to stats.
Well, for my Lupe, when I look at his stats, his HP is green and full, but under it the Attack is yellow (241), and the Defense and Agility are red (156 and 133, respectively). His Intelligence is also green (981). For my Chomby, there's a yellow Intelligence line at 231. I have to assume there's some point between 156 and 231 where the red line will turn yellow and, similarly, some point past 241 where it will turn green.