Figures do not have a FontSize property.
If you
set(text())
then you will see that there is a property named 'Color'.
Generally speaking, the graphics command documentation for a low-level object will have a reference to the place you can find the (documented) properties for the object. For example, http://www.mathworks.com/help/techdoc/ref/text.html says near the top,
For a list of properties, see Text Properties.
There are also undocumented properties. For more information on those, please see Yair's blog on them