The first pack, due on the week of Sept 6th, is the fairly self-explanatory (and immediately repulsive) "Color Pack 1." The first of several makeovers, it'll add 7 new colors per character, though these will not be saved in replay files and will not be viewable by opponents who don't own the DLC. It's up to you to describe the many ways in which they're missing out.
You'll also be able to download music packs, which add tunes from Street Fighter III's older entries (New Generation and Second Impact), within "the next month or so." Lastly, Capcom's planning to use "Match Pack" DLC as a vector to satisfy spectators. Two packs offer an hour's worth of content each, drawn from high-level matches saved during a "semi-secret" Capcom tournament and paired with commentary by James Chen. We'll learn more about their price and educational value later in the year.
