As requested here: https://teakdoor.com/photoshop-stuff/...-shop-pro.html
Step 1:
Zoom into your chosen picture by 300% or so, then select the Freehand Selection tool.
Step 2:
Use this to draw around the object that you want in colour...
... and you should be left with something like this:
Step 3:
Invert the selection (Selections > Invert).
Step 4:
(Adjust > Hue and Saturation > Colorize)
Step 5:
Set both to "0".
Step 6:
(Selections > Select None)
Step 7:
Hey presto! You're done. (But hopefully you'll have chosen a better picture than I have so that the effect stands out a little better. )