I’m afraid you won’t be able to customize the look of the notification emails. There is no interface or option allowing you to do that right now, and inline styles will be removed from the notification emails.
You can, however, customize the contents of the emails by going to Settings > Reading in your dashboard. You’ll find options to customize the email text at the bottom of the page.
We’re also thinking about adding some design options in the future. You can follow our progress here:
https://github.com/Automattic/jetpack/issues/2437
