I just got him and I pretty much have a design that is pretty self-explanatory for being boring and forgettable. but I need a species and color that sort of matches the theme or name. Should I just leave him as a common pet, or scribble? I know usually when people stock pile names it's often a bunch of Kumos. Maybe a common Kumos? Any thoughts?

Great name, congrats! My first thought was a scribble pet, although a common Kumos sounds like it would definitely fit with what you have in mind. Although the scribble Kumos is the same color as the common, so maybe that would be a good choice?

i could see something scribble working...

I think the common/scribble Kumos is a good idea, since it is the most popular pet (ie. most generic). It also was once used as the error image and is sort of a mascot for Subeta (so it would pop up often without being your pet, again making its appearance a common occurrence (which could work with your idea of boring and forgettable, since it's so common.)). So I think in the context of Subeta that works quite well.

Another option is making the pet the blob experiment, which will be a regular pet option at some point. This pet is more objectively simple. The kumos is still like a wolf, with a face, fur, muscles and bones, different types of cells, etc. So actually a complex animal in real life. The blob pet is just a mass of goo with eyes.

I think scribble 5162 fits the description "boring and forgettable". I mean, just look at it xD