I really just play around with layer modes. Once I kinda have my final B&W version complete I make a new layer on top of that and set the mode to 'Color'. I lay in my base colors to try and get the mood down. Then depending on my lighting I'll add a Multiply/Overlay/or Soft Light layer. Really I just mess around with it til I get the look I want. There is no wrong way to do it. Normally I'll adjust it all with some curves and color balance and then maybe another normal layer on top to pull out some more color details that I didn't get in the B&W version. Hope that helps!