yes there are brown good and bad, and most green are bad. I dont know of a green predatory one off the top of my head but they maybe one that i am not thinking of from the family Pentatomidae.
Try watching them and see what they do, feed on the
plants or other bugs.
Also beneficials tend not to hang out in large numbers together (many will eat each other) so if you have a bunch of the same ones together most likely they are
plant feeders.
For the mouthparts I am sure it was its proboscus, its tong. they keep it rolled in its mouth until they unroll it to feed.