Use the following steps. Surely there are other ways, but this is what I used.
1. Open photo
2. Ctrl J to duplicate layer
3. Create Adjustment layer > Hue/Saturation
4. Drag Saturation to "0" to change to b/w (you mush uncheck colorized)
5. Fill layer with White (Ctrl backspace or Alt backspace depending on your foreground/bg colour)
6. Brush tool - select black
7. Paint over area to review colour behind.
8. Flatten layer
If it's just one solid block of portion of the photo that you want to select in colour and not many parts, here's what i do, it's simple:
i) use the lasso loop to select the portion that you want in colour.
ii) from the selection tools, choose inverse selection
iii) use desaturate. It's done!:bsmilie: