Coming with Mission 07, there are some new accessories that you will be able to freely equip and colorize on your captured characters. Here are some examples of the sort of outfits you can create. I will continue adding more accessories in future updates to the game too.
In addition to the new appearances, you will now be able to see your customized characters with the new "call reinforcements" feature. While playing a mission, you will have the option to spawn any of your captured characters at any moment. You characters will help you fight the enemies. Be careful, though, because if a character dies, and you complete the mission, it will be gone forever!