Don’t get too worried right away. The fluid will turn brown again, that’s normal, but the reason why is what’s important. You may have driven enough miles to be ready for another flush no matter how long it’s been. Or you may have over heated the transmission, this can happen very easily. Getting stuck in snow and spinning your wheels can cause this. Also a poor cooling system can burn up transmission fluid. Check to see how many miles have been driven since the flush, and try to remember if you’ve done any harsh driving. Have the technician check it for you the next time you have your oil changed. The worst case scenario is you will have to get your next flush a little early. Remember, transmissions are expensive, maintenance is cheap.