There are five ship styles in the game: Altarian, Drengin, Human, Torian, and Yor. The ship style you choose when customizing your race determines what your base hulls look like and how the game's base ship designs appear. The choice of ship style is purely cosmetic.
Remember that when starting a game that your hulls will never appear for another race unless you use that same race hull base.
In Dark Avatar, each race got their own ship style, bringing it up from five to twelve. Note that some ship styles are based on the same hull base, so (for example) saved ship designs for Arcean Empire will appear in the game for Terran Alliance.