In addition to selecting your parts, you can select the color of your armored core (part by part, not just as a whole) and your weapons. You can even create your own emblem to adorn your armored core: use an existing one, edit an existing one or make one from scratch. If you have a USB mouse, you can hook it up to your PS2 to make your emblem editing a lot easier and quicker.
The UI feels similar to previous Armored Core games, and maintains the same style throughout all of the menu systems. The customization opportunities doesn't stop with the selection of armored core parts and weaponry, either, but extend to the heads up display when you're actually playing the game. You can change the color of the HUD and select which items you want to display and which ones you don't.