Reading your replies it doesn't sound like you have your sous vide circulator yet - you say it's still shipping - YES, it will improve the coloration. The whole point is that you cook the cut totally, all the way through, at a low temperature, and then sear it PURELY for the flavor the maillard reaction (browning) lends.
I'm going to echo the call for butter above - unlike straight vegetable oils but similar to mayo, it has a combination of necessary fat and optional sugars, which give you a better brown. (Unlike mayo, I actually keep it in stock.) The other upside of using butter specifically is that you know it's hot enough when the butter itself starts to brown - since you'll only need thirty seconds per side, the butter won't be excessively brown by the time you pull the meat from the pan, and that means it's a great time to add some mostly-cooked grains or vegetables for a lush side dish, or warm wine to make a pan sauce. If you aren't sure the grease is hot enough, flick a TINY water droplet at the pan - if it zips off screaming, it's there.
A little more oil could also help - it doesn't have to swim, but you want a good puddle, not a thin smear (yet more reason to then soak it up with some sides - I've even used plain bread for that if I'm doing a roast as it makes a killer sandwich.) You can use a brick or lid to press the steak into the pan for more even contact with the sizzling surface, but I usually just depress it with the tongs I'm handling the meat with - it's only a little over a minute of effort, your arms won't get tired.