Also, I'm not sure what details could be secret right now. Nike and the Seahawks have both been pretty vocal and public about their progress and ideas.
A few more details I know just from reading press releases and listening to ESPN, and from various sources related to Nike and the Seahawks (and all of it has been public):
The "alternate" uniform is likely to be the "blackout look": all-black or dark monotone uniform, likely with Seahawk Green highlights. Supposedly not quite as florescent as the Oregon "O" on their blackout uniform - more of a neon green. At one point, the team had experimented with green numbers, and also matte-black numbers, but both ideas were nixed.
The Seahawks will be the first NFL team to get the Pro Combat look. Phil Knight was personally involved in that decision, just as he was with Oregon being the first NCAA team to get the Pro Combat uniforms. As with Oregon for the NCAA, the Seahawks will be Nike's "proving ground" for the Pro Combat look in the NFL. They are hoping to get it perfect because they want to sell it to the whole NFL. There is a HUGE amount of money involved for Nike.
The Seahawks have stated they want to keep a dark blue monotone look for the home uniforms. They really like the all-navy-blue look. Expect to see something not too drastically different. One thing I've heard from Nike sources is that the home uniform is going to be more monotone than now, likely with a matte-finish or carbon fiber helmet and possibly with matching matte black/grey shoes. A big part of the Pro Combat look is monotone and two-tone color schemes with matte finish and Nike has been pitching that hard to the Seahawks.
Green is likely to be used primarily for highlights. That has come from many many different sources, including one of the Seahawks front office staff who said it on-air. They've said the reaction to the lime green jerseys was far worse than they anticipated. They had hoped to tie in the Sounders/Seahawks merchandising with a unified look, but it's clear that football fans don't like the green. They are moving away from green in the uniforms and if we see it, it will likely only be in limited highlights, perhaps sleeve stripes, etc. It will be minimized and they had moved away from green as a primary color (for jerseys, pants, helmets, etc) as of last summer.
I'd be wary of anyone who claims to have definite and exclusive info about the uniforms. Nike has multiple design teams working on the design, and so do the Seahawks. The Seahawks and the NFL have been very hands-on and apparently they won't be able to be as dramatic as the NCAA redesigns.
And again, I wouldn't believe anything as being "final" at this point. Just a few weeks ago there was talk that Nike had started all over with the Seahawks uniforms, for about the 100th time. The dude I know from Nike told me they have literally gone through dozens and dozens of different designs, and there was some concern that too many cooks in the kitchen was impeding their ability to meet their release deadline. He said they couldn't even get a final consensus on the design of the numbers on the jersey.
I'm also anxious to hear what details BFS has learned. Not sure why people are attacking the posters who are frustrated with the lack of details. That is understandable. We're all anxious to see the new Pro Combat uniforms, and any confirmed details would be great. If you have details, share them please. Thank you!