Chrome bumpers are on LT and LTZ
RST and Custom have body color all around
Trail Boss is all blacked out (grille, bumpers, door handles, mirrors, etc)
High Country bumpers are body color but the grille is chrome with bronze ends
Z71 does not make the truck all body colored anymore.
According to Chevy's site, Z71 includes the following on an LT:
Bed Protection Package
Dual-outlet exhaust
2-speed Autotrac Transfer Case
Hill Descent Control
18" Bright Silver painted aluminum wheels
Rear wheelhouse liners
Chevytec spray-on bedliner
Automatic locking rear differential
17" P265/70R17SL all-season, blackwall spare tire
Skid plates
Trailering Package
18" P265/65R18SL all-terrain, blackwall tires
High-capacity air filter
Hitch Guidance
First and second row all-weather floor liners with Z71 logo
If you are looking for all body color, you will need to order a Custom (WT) or an RST. If you want body color bumpers only, you will have to order the High Country. If you want all blacked out, you would either have to order a Trail Boss or a black Custom/RST. Keep in mind the blacked out bumpers on the LT Trail Boss are not painted black, they are very dark black chrome along with a gloss black grille, handles, mirror caps, etc. Trail Boss also is the only one that comes stock with blacked out Bow Ties, both the front one and the steering wheel one.
Below is an Image that GM-Trucks took of all eight lined up and a link for a video commercial that shows all 8. Hope this helps. Let me know if you have any other questions.