Someone on the OK K.O Reddit pointed this out to me when I mentioned K.O's eyes being darker during a certain part of the promo. (vvvv)

They said the same thing happened in the episode You're Level 100! and that the shadow under K.O's eyes, if you look closely, isn't actually a shadow, but eyebags or something like that. (I looked closely, the darker shading under the eyes goes over the actual shading on the right side of his face.)

Yeah, also K.O looks to have purple flakes around him on the image from You're Level 100! and people that watch the show know that his attacks are supposed to be blue. In the promo, the attack he does is purple, when it should be blue. (vvvv)

They said that they think K.O's shadow self or him being evil might actually have something to do with this.

Holy crap my mind is actually blown right now. I'M ACTUALLY QUESTIONING THIS RIGHT NOW! LIKE WHAT THE HECK?!?