Using different RGB input for B&W output (orthochromatic effect):
Basic : Add 2 serial nodes:
Node 1: pull down red in Cruve to 0 (cyan color look)
Node 2: Saturation to 0
Play around Luminance Mix (L.Mix) from 0 to 100 in Node 1, it affects the darkness of image
Advanced: (just create 1 node):
Apply RGB mixer in Node 1, tick Monchrome box
Play around the R, G and B Output bar to give the B&W effect
Remark:
If adjusting the original footage color temperature (e.g. from -4000 (cool) to 4000 (warm) ) give very different RGB mixer result
Also, make S-curve on original footage should give better result too.