Nutrient levels, flow issues are often a major part of coloration, IMO.
It's not uncommon for Acropora to brown when introduced into the tank, remain pretty blah while encrusting and only recolor well when they start to grow from their tips again - but then again it shouldn't be every Acro doing that either.
Skimming will definitely help, paying attention to water quality is neverending with Acropora. There are Acro's that are browner [or brown] - and colorful corals that appear brown now can be made colorful again IME. Some Acropora come in with one coloration - change in your tank do a different one. It's a crapshoot to a degree - though I've found that with good water quality, colorful corals remain colorful - just sometimes change colors a bit.
I've had far better luck with tank-aquacultured stuff than wild for keeping good colors ... and a few have required a 6 month wait to do much ... genetics is important to having a nice tank, but the right tank seems to be able to make just about every coral a star.
Anyway - do check out the `lets talk about' threads in the SPS sticky FAQ:
http://reefcentral.com/forums/showthread.php?s=&threadid=421812
Great reading. Note that water quality is the first listed, though flow and light are also key.
I would perhaps consider 10k bulbs as well. While the 6500 has the best output [I use on my frag/non-display tank] I think to the eye 10k gives nicer color [widest range]. And various 10k bulbs IMO look different - research, ask around, see as many as you can. IMO, this is the second thing to pay attention to.
