Have you looked at the current transfer thread: http://talk.collegeconfidential.com/brown-university/1833116-official-brown-u-2016-transfers.html#latest
Or the previous ones: http://talk.collegeconfidential.com/transfer-students/1746562-official-fall-2015-brown-transfer-thread.html / http://talk.collegeconfidential.com/brown-university/1605372-official-fall-2014-brown-transfer-thread.html
Anyway there seem to be a lot of threads about specifically transferring to Brown on here! Dig deep…
Can’t claim to be an expert for transferring, but I’ve applied for the Fall 2016 round and am waiting to hear back, so I’ll just give my two cents. In general the more distance you have from HS at the time of application, the less significant your HS stats. I cannot comment on how exactly Brown views it though, because on their transfer page they do put HS stats as one of the key components of how they will evaluate you as a transfer applicant.
I sympathise with your reasons for wanting to transfer to Brown, but for admissions purposes they don’t seem to be specific to Brown enough. A lot of other institutions can fit that description, and you want to make sure to emphasise in a focused and well-researched way exactly what resources at Brown and what parts of its experience you would glean from/contribute to. Having a strong and persuasive rationale is definitely one of the most important aspects, if not the most important, to your application.
Other than that, I believe transfer admissions looks for people who have excelled academically (a lot of what I’ve read point to 3.8 as a competitive benchmark/average for Ivy transfers, but I really don’t think it’s an absolute must in any sense) and contributed significantly to their current campuses/communities as a leader/peer. I think they also look for people who are resilient and full of initiative, who have a can-do and self-starting attitude. Brown’s intro paragraph on the transfer admissions website is actually pretty spot-on - take a look if you haven’t already!
Obviously there are more nuances to the whole process that are oftentimes outside of your control, like what specific class spots they are looking to fill in any given year, the very unfavorable odds and etc. The important thing at this juncture is really to do enormous amounts of research into Brown or wherever else you are applying to, and concentrate on significantly involving yourself at Colby and during your year off, using every resource and taking advantage of every opportunity available to you. Remember also, quality over quantity!
I don’t feel comfortable “chancing” anyone here because I don’t have a complete picture and I can’t speak for Brown or any other college. However I would echo previous comments and say that your H.S. stats and extracurriculars look promising. Good luck, and let me know if you want to chat more.