I have to be honest, that was a bit of a confusing read, but thanks :P
And depth can easily be achieved by having a (slightly) blurred background with less contrasts than the characters in front. Also, the objects in front usually have darker values.

So to keep it simple
Close - darker colors, sharp edges, consider higher contrasts but be careful with it
Background - blurry, lighter colors, much less contrasts, simpler shapes

Although, this is art, so none of these rules are "set in stone" and there's plenty of exceptions out there.