Brute Majors are the next stage of technology that brutes develop in there campaign of Grunt molestation. Their bluish armor represents their mental incapabilities: everything.
Ensemble Studios were going to make them the weakest unit, but Covenant Species Protective Services didn't allow it because of the following reason: Crap. Sorry, that was the most common for silencing them, the reason is they thought it was torture.
After the dumbass Testicle-chins exiled the Arbiter, the Brutes started to unite. Since most of them are dumbasses and doesn't what a Spike Grenade does, they were unorganized. They got owned when Master Chief came to one of the Covenant capital ship and owned Prophet of Mercy until Gravemind came and made the prophet into one of his Peanut Butter Sandwiches.
What is there to say? They're weak and will die within 4 to 5 hits in their face, just like the amount of times they fell on their head during childhood (no wonder they're fugly and retarded).
These brutes are not actually violent and they are very good with conversations. In the Battle of The Top-Dog Hula Hoop, one Brute Major, wrapped his arm around the chief's head and said "All right mate!" only to get punched in the face by the chief for embarrassing him.