I think that parking in some Walmarts is 'legal', but you want to not stand out as being an obvious inconvenience. Like one comment above, by leaving a light footprint, and not standing out, legal parking can become illegal eventually. For instance, we, as RV'rs would instinctively park far from the Walmart entrance if we would (probably) take more than one space, and most consider it good form to not use slideouts in order to be less 'obvious', even though legal.
I still think the flat tan to brown colors would work in many outdoor locations. When I'm counting my cash from the ATM, I try to do it in the least obvious way, even though it's legal, and it's mine to do however I want. Because of other people, not hiding from the law.