Just popped back for 5 minutes to explain the process I went through:
- Desaturate the original image (Image - Adjustments - Desaturate), CTRL+SHIFT+U[/*]
- Select the HISTORY BRUSH from the brush palette.[/*]
- To should have a HISTORY palette on the right of the screen. Click in the grey square to the left of the history action BEFORE the 'Desaturate' you have just done. NB - if you have only opened the file and desaturated it, click the grey square to the left of the thumbnail of the original image at the top of the history palette.[/*]
- You can now paint the previous state over the desaturated image, choosing your brush size carefully and zooming in to accurately re-colour tricky parts.
Hope this makes sense. If not, give me a shout and I'll try and explain further.