Showtime had different eyes at a time 0: and he looks younger and more innocent. I've noticed how a lot of your characters change in their appearance as they grow up. For example, Writer (when he was young and alive) had a brown based pelt, and now you see him with grey-ish and green-ish colors. Then again that might be because he's sharing a body with another dog xD as for Oxymoron he might've been changed when he was taken when he was younger? I'm not sure I know all of the details
Showtime is one of those technicolor character designs that's still easy on the eyes. I chock it up to good use of color theory but there's more than that. Showtime is full of naturalistic tones that feel like they could be real fur colors. They are vibrant, and varied, but they all fit together in this coherent way that leaves them looking "right". That the design can showcase contrast and harmony together that way is a great achievement.