Separation of colored areas from monochrome

You could make a saturation map* then use that to make a mask that shows the colour then duplicate the layer and invert the mask to show greys.

*To make a saturation map:

a. Add a Selective colour adjustment layer

b. Step through each colour and set the black slider to -100  (Absolute)

c. Step through the white neutral and black - and set the black slider to +100 (Absolute)

Your image is now shows as black where there is no colour through to white where there is fully saturated colour.

It is easy to make a mask from that (adjusting the threshold as required ) to show colour and inverting it to show grey

Dave

You could try Select > Color Range. Then cut and paste the selection on to a separate layer.

Is this what your looking for?   https://youtu.be/A44ybqF8Jzc 

Or this  https://youtu.be/sLZnKVjxSJg 

This is exactly the reason whi Posted about using a Tablet or Laptop touchscreen. I'm a Subscriber to a Canon magazine and it had step by step video on how to do it and I wanted to try it out but with only a laptop mousepad i find it hard to control the brushes etc. Wish I could share the video but I can't. I'll see if there's a similar one on YOuTube i can show you mate.