Snakes were generally treated as positive or at least important in the carvings and the codices. Think of the vision serpents for example. The two-headed snake is used in Maya iconography to represent the ecliptic. I don’t know why they are shown with their mouths open, but of course a vision serpent must always be opening wide to dispense the wisdom of the ancestors. Why three sets of teeth? I don’t know that either, although if I knew my herpetology better, it might identify the species.
The Milky Way is sometimes associated with the world tree, and is depicted as green. The trees here are based on those found in a couple of ceramics where the hero twins as shooting Itzam Ye in the tree. I was wondering why they were drawn that way, until I checked them against my sky atlas. There they were in the Milky Way, with the features show and the standing at that angle to the ecliptic at the two crossings.
Yellow is the color of the South of SoPilar.