Hi Keith -- cool -- I've never seen one in person myself. Humbolts are Dosidicus gigas a.k.a. jumbo squid. Seems there has been a population burst of these guys on the southern coast of California in recent years.
Not a lot, divers breathe pressured air, hardly ever pure oxygen
Divers should always attempt to keep their Fio2 below 160 kPa (On a more serious note)
But all jest left aside, Dosidicus has been shown to be fairly aggressive, hunting en masse. I think using the term in packs suggests a level of social interaction between the squid that I'm not 100% sure of. Whether the flashing of colour indicates communication with other squid or merely a mesmerising factor towards intended prey items, I am not sure of either.