Hi Ricardo,
There is no exposed formatting, however the rich text engine internally supports per text fragement background and border. We implemented the required parsing and this functionality will be exposed via the following attribute names:
back-border
back-bordercolor
back-borderpattern
back-borderfactor
back-borderwidth
back-color
back-gradient
back-image
back-pattern
back-hatch
the meaning is the same as with the fore ground counterparts which are documented. The SP coming up next week will feature this functionality.