As far as I know it doesn't matter what colours are used. I would always keep RED/Black as a pair and BLUE/BROWN as the other.
As long as you keep the same colour coding for the entire system it will be okay. If your return is Red/Black keep all returns as red/black.
For a B Class system I always use the RED/Black as the signal circuit and the other pair as the initiating.
LVT is not FAS cable. FAS has 300Volt insulation while LVT has 30Volt.
