One of the features added to version 2.3 of our Android, iOS, and Desktop clients is support for HTML messages to style text. By sending messages to our API with the html flag set to 1, HTML tags in the message body will be interpreted by our apps and be used to style text. The current HTML tags we support are:
<b>word</b> - display word in bold
<i>word</i> - display word in italics
<u>word</u> - display word underlined
<font color="blue">word</font> - display word in blue text (most colors and hex codes permitted)
Due to the way notifications are handled on most platforms, HTML tags are stripped out when displaying notifications (leaving just the text content) but are shown inside the Pushover app once the client has synced with our servers.