Hi Francesca,
You should take a look at
http://sitepainter.sourceforge.net/documentation/index.html for
information about this. Anyway, the way SitePainter works is that it
looks for close path figures, rectangles and circles, in your case you
do not have any of these. My suggestion is to load the image in
SitePainter and then create a new shape, left menu; then you can use
the right menu to check the name of the elements (Elem.). Note that if
you double click on the name element, right menu, you can edit it.
When you color, SitePainter searches for the sample names that are on
your data file and matches them to your element name, elements that do
not match any sample name will be "ignored".
Cheers,