The Boov can change color when they're under extreme emotion.
Red - angry.
Green - lying.
Yellow - scared.
Blue - sad.
Pink - love.
White - overwhelmed and/or shocked (usually faint)
Brownish Yellow - disgusted.
If the Boov listen to music, their bodies automatically dance to the rhythm.
The Boov seem to be perfectionists, as they have a rule "9 mistakes and you're out."
The Boov do not touch each other on purpose.
The Boov are not all the same shade of purple. Not taking into account their color change when showing emotions, their skin seems to span a range of different shades (this is particularly easy to see during scenes on the crowded ship). It appears that there might actually be seven different shades of "normal" Boov skin tones. If that is the case, it might be a nod to the seven different Boov genders that are discussed in the book that the movie is based on (Adam Rex's "The True Meaning of Smekday").
The Boov are highly omnivorous, and can ingest almost anything that humans would find inedible. They also seem to enjoy the taste of rubber.
Boov possess grammar that is somewhat juvenile compared to that of humans.
Boov have skeletons made primarily of cartilage.
In the book, their shirt color indicates their job (notice on Captain Smek has an orange shirt), they sent us to Florida until they found out oranges (referened by Smek walking around Paris wearing oranges), they had guns that literally wiped things from existance (notice that none of their guns are ever fired), and they had a song insulting Gorg. They also abducted people not to relocate them, but to learn the human language (Tip's mom was sent back, just not where they found her). Oh was specifically tutored by Tip's mom, which caused mistrust between him and Tip.