UPDATED: Here is a link to a photo slideshow of the Seahawks new uniforms, their home, away, alternates, and a few different uniform combinations with contrasting jerseys and pants. Here are some photos of the Seahawks uniforms you'll likely see them wear most of the time, courtesy of Seahawks.com:
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Here are some of the alternate uniform combinations - I'm not really sure how often these will get worn because I do believe the NFL has rules that limit the different combinations you're allowed (though maybe someone could quote the rulebook on that because I'm not sure), but they're fun to look at nonetheless.
BLUE JERSEY, GREY PANTS:
BLUE JERSEY, WHITE PANTS:
GREY JERSEY, BLUE PANTS:
WHITE JERSEY, BLUE PANTS (AKA THE CHARGERS)