Since the first version of LPX, Apple has changed the location of the tif file “ani_background” that is the background of Drum Kit Designer, but you can still modify it. It is in here:
So, back-up “MaResourcesLg.framework” (or the whole Logic app) and replace the tif with your own or with some of these, for example. Three options from black & white to yellowish (the latter two quite close to each other):
Drag one into the folder seen above and click “replace”.
A bonus: brown one.
Ps. There is also Animal one, ask it from this person: https://www.gearslutz.com/board/10762198-post2867.html