The two letters at the end of any colored part that comes in more than one variation, are a color code. I have learned over time there are a few used in the 3G Impreza. Here is what I have learned:
ME light gray
JG Dark gray
From that you can see the "ME" parts are going to be the non-STI light gray. Previously to '11 the black STI parts for a sedan would not have been carried by SOA but they should be now. A guess on the color code for those would be "JJ" like the previous STI hatch, but you are best to look them up or have your dealer look them up for you.
BTW if you are converting to the dark trim, there are a umber of smaller parts, such as the "SRS" bolt covers on the pillars, grab handles and their bolt cover trim etc. that need to be converted to the blakc version as well.