Suggestions: are there any limitations to what skins, decorators, and decals can be suggested?

(Sorry if this is the wrong section.)

I’m aware that basic rules apply (nothing inappropriate), but are there any requirements/rules for what can be suggested? Does it have to be something real? Can it be Something you made up? (such as model kit paint schemes/drawings) I’m asking because there are no rules stated about what’s valid to be a suggestion for that section, unlike the vehicles sections.

@leroyonly