* when any colours are changed, the menu text disappears unless you hover over it
* selecting any font option for body text makes no changes
These issues might be browser related. Do you also encounter this issue in a different browser? for example Firefox, Safari, Internet Explorer, or Google Chrome?
* the post title font is always bold despite selecting other options
* there is no obvious option to change the colour of the post title
For certain elements it's better to use CSS. To learn more about how CSS editing works at WordPress.com, see this help page: http://en.support.wordpress.com/custom-design/editing-css/
Most of our CSS support is done in our community forums by both staff and volunteers: http://en.forums.wordpress.com/forum/css-customization
When you create a CSS-related help request, please make sure to select or link to the WordPress.com blog you're working on and include a clear description of the change you're trying to make. It helps a lot.