Wikipedia has a great site for howler monkeys and gives an audio of their sound.  I was hoping that the mayan word  chuwen, would sound something like the gutteral vocalization that these new world monkeys make.. but this wasn't so.  In this mayan glyph for the 11th day of the tzolkin calendar turned into a stained glass pattern to make for schools and kids rooms did not immediately look related to its meaning, however, I decided I thought there were haunches in this glyph, and that the light area at the top was the light coloration above the eyes of the howler monkeys.  Maybe a stretch but it is what I could come up with.  LOL. 
I put the monkey in the green of a tropical canopy with a blue sky.