"I remember Halo attempting to go with the canon route for MP 1 time: Halo 4. That's it. Well, mostly. Fotus, and Raider were in there. Every other game had hilarious gametypes, customization options, and general MP wackiness, and somehow we still took it seriously. Why are you singling out Halo 5 when it's not the first time for it to happen? Halo 4 still had absurd modes, but did we take it any less seriously? Without it it's no fun. Do you not like fun?
I could easily come up with headcanon saying that those wacky skins are for Spartans who are outside the restrictions of the Spartan Branch, and can do whatever they want with their armor/weapons because they're just badasses. We've already seen plenty of canon spartans wearing the entire rainbow, so is it crazy to think the weapons would be just as vibrant too?
Another explanation is skunkworks productions (343 loves this excuse). "This Pizza AR is trying to test if having a delicous looking pizza on your gun would make enemies hungry, or distracted by looking at it: increasing your chances of success in battle" idk.
Sorry if I'm being redudant, or repeating arguments here and there. It's kinda hard with this wall of text you made, and it's really late."
-@SelfDestruct
Yes, this 100%... I mean let's not forget about the flaming helmets, or confetti or hearts coming out of Spartans. Or maybe skulls in helmets in Reach...