There are no rules, use what you like. A step up in sheen on the trim makes it "pop" a little, even if you use a different color than on the body. If you want a slight contrast use Low Lustre on the body, and a Satin Finish on the trim. For a bit more "pop" substitute Semi Gloss for the Satin. I like the look of Semi Gloss on doors windows, shutters, etc. typically a different color than the body of the house.