What I think we're looking at is a highly mutated subspecies of hominid; possibly evolved from Gigantopithecus or a relative of that long-extinct creature. Why Gigantopithecus?
Because that prehistoric ape is related to (precedes) both hominids and orangutans, plus it had a very large size.
Furthermore, an orangutan's diet is composed of 90% fruit, and if this species is or becomes the same way, it's not hard to see them eating a lot of fruit with natural alcohol (which could naturally ferment inside their digestive systems, as with sauropods, which would generate alcohol inside them) and evolving to have a high alcohol tolerance and/or affinity.
Since plenty of supposedly obligate herbivores, like deer and even cows, can and will eat meat if they have the opportunity, it's not hard to see such a species evolving to be omnivorous after some evolutionary trigger; perhaps new herbivores evolved that made it almost impossible for them to obtain all the fruit they need, so they began preying on them (since there were more herbivores than fruit) and gradually became omnivorous.
At this point, these creatures have evolved into ape-men, and possibly interbred with Neanderthals, becoming the primitive Oni. Their red or blue coloration comes from the fruit itself; carotenosis results in humans from an excess of dietary carotenoids (carrots, oranges, sweet potatoes).
In this case, there are two similar species of fruit, both of which have a specific effect on Oni physiology if eaten; plants with the red fruits evolved to have a defense like the acacia tree and ants (ie. Oni eat the fruit and special chemicals cause them to become addicted, aggressive, and territorial, therefore providing protection for the plant). Blue fruits, however, contain chemicals that enhance cognitive function (plausible; since foods high in lutein and zeaxanthin, which are both pigments, have been linked to increased crystallized intelligence).
Both of these fruits are frequently imbibed by Oni after first sampled, and the resulting buildup of pigment turns them red or blue. As for the Oni horns, that can be explained by Shope papilloma, a form of cancer that causes the afflicted to gain horn-like growths.
A benign form of this cancer may have resulted in horned Oni, and since horned Oni did better in fights over mates, Oni today all have horns.