I was fortunate to receive a color vision medical waiver for USNA last spring. Like 1985 said, there are only a certain number of waivers that medical is willing to award, though exceptions are made. My roommate for plebe summer actually failed the color vision test on I-Day (no previous problems) and was granted a waiver within an hour, no questions asked, so the waiver process is "ambiguous" to say the least.
If you're a very qualified candidate and you got your DoDMERB results in quickly (i.e. last fall, January at the latest), there's no reason to believe that you shouldn't get a waiver. Considering that BFEs and TWEs are beginning to trickle out right about now, most of medical's allotted waivers have probably been exhausted, unfortunately. Time is the enemy.