Bold  fonts are used for emphasis. Since color is almost universally available, there are

lots of options to change colors (foreground and/or background), but without conventions

we can't know what a particular color means without rtfm.  Choosing colors is not

simple as you need to accommodate various forms of color-blindness.  Text-to-speech

systems would have to be rewritten to detect color changes.  Some of the technical

problems could be handled by relying on underlying semantic markup and treating

terminals and text-to-speech as different rendering systems. 

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