It should be no surprise to learn I am a huge fan of Rob J. Hayes work. I am a fan of every series he's done and while I prefer his Best Laid Plans duology to The Ties That Bind, it's not by much. The Colour of Vengeance is the best of those three novels and I think that has a large part to due with the fact its protagonists are entertainingly psychotic.
The Black Thorn (Betrim to his friends) is a somewhat realistic take on what a person with the Chaotic Neutral alignment would be in real life. He has poor impulse control, an incredibly violent temper, and is an utterly savage killer but isn't adverse to doing the right thing. It's just his loyal to his friends trumps any form of ethics the man may have and the "right thing" in societies that feed on slavery and oppression are rather murky. This is a few millennium before civil rights would become a thing.
Indeed, if I were to describe the character, I'd say he's pretty much a man born with a dog's soul. He's loyal to a fault, friendly, as well as eager to do right by his people but viciously attacks if you go after his family. The Black Thorn makes numerous mistakes throughout the novel from his following up on his instincts, some with dramatic consequences, but that just makes his story all the more entertaining.
The contrast between the Black Thorn's "emotional morality" versus society's ingrained morality is best exemplified by the character of Pern Suzku, a Hyborian Age ninja who follows a absolute code of bushido that is pushed to its breaking point by the fact he is assigned to work for a Caligula-esque monster. This particular monster, Swift, is fascinating because he's actually a supporting character from the previous book which was implied to have done terrible things off-camera but we only now see as the depraved horror show he is.
This is very much a novel about Evil vs. Evil but also a question of who defines that idea. The Black Thorn, Henry, and newcomer Anders are pretty terrible people but they live in a pretty terrible society. They're also faced against the kind of organized industrialized evil which will make our own world a place of massive suffering in the future. It's very much the kind of story Robert E. Howard would have enjoyed, though a bit less idealistic about barbarism.
Swift makes a great villain as he's the kind of person who exemplifies the "want, take, have" mindset which the Black Thorn exudes but shows none of the loyalty or general kindness. Having become a powerful crime lord since the events of the first book, he brutalizes and enslaves with absolutely no hesitation simply because it makes him rich. One of his most loathsome moments of the book is when he casually has his girlfriend tossed in a pile of slaves to be sacrificed because he was short on a quota and the money was too good.
I think my favorite character in the book is probably Henry, the demented murderess who serves as Betrim's unfailingly loyal companion. Her semi-consensual relationship with Anders (basically a drunk nobleman she kidnaps to be her boyfriend) is a source of black comedy throughout the book. I think Henry deserves her own book, really, and is probably my second favorite character in the series after Jezzet Vel'urn.
In conclusion, if you're a fan of grimdark or Sword and Sorcery tales of the violent buccaneer set then this is probably a book to pick up. Not all fans are going to love the characters or their amoral ways but those that do will want their adventures to continue.