can you add colour to a specific area of a black and white print

Yes, that's something you can do, though Inkscape isn't necessarily the best tool for the job. Though it can incorporate raster images, such as photographs, Inkscape was designed as a vector image editor. While it excels at editing vector images, its abilities with raster images are more limited (and appropriately so). Therefore, depending on what exactly it is you want to colourize, you may find it better to use a raster image editor such as GIMP.
I'll tell you ways of colourizing a photo in both programs though, so you can make up your own mind which will be best for you.

INKSCAPE
Import (File > Import...) your photo.
Adjust the document size to match the photo. (Don't resize the photo to match the document size—that'll change the resolution.) Go to File > Document Properties to adjust the page size. You can get the photo's size by right-clicking it and choosing Image Properties.
Centre the image on the page. While the Image Properties window is open, you can do this by changing "X" and "Y" to 0.

Draw a shape (e.g. a circle for the ball) over the photo.
Adjust the colour and opacity to produce the correct colourisation. Go to Object > Fill and Stroke... for this. Clear the stroke and change the Fill colour details.
Repeat for any other areas to colourize. Use one of the line tools for more complex shapes and remember to close the loop. You can always edit the shape later with the node tool.

GIMP
Open your photo.
Add a new layer (Layer > New Layer...) You should see a second line appear in the layers dialog, called "New Layer".
Click the eye next to the "Background" layer to hide it.

Click the "New Layer" layer to ensure it is selected.
Choose the Fill tool from the Toolbox dialog (it looks like a tipped paint pot).
Choose a colour for colourisation.
Fill the new layer with your chosen colour.

Reshow the Background layer by clicking the eye again. You won't see it yet because the coloured layer is on top.
With the New Layer selected, slide the Opacity slider just above the layers list to the left. You should see the photo appear, completely colourised. Adjust the opacity (and refill the layer with another colour as necessary) to get the colourisation right. Don't worry that it's applied to the whole image for now. That'll be changed next.

Right-click "New Layer" and choose "Add Layer Mask...".
Click "Black (full transparency)" then "Add". The image will return to black and white.
Change the selected colour to white, and choose the brush tool.
Wherever you now paint on the image should become colourised. If you make a mistake, change to black and paint over it. That part of the image will return to black and white.

For simple cases of raster image manipulation, you'll probably find that Inkscape is sufficient. For more complex ones, it's generally best to use a dedicated raster image editor like GIMP.