If you are only outputting something with the input then you are on a right track when you want a "outputTextArea". But it is not needed in
JSF since you can always use outputText. So why can't you use outputText? If you absolutely need the input to be actual html textarea you can just use plain html textarea and put the inputText inside it or something similar (like fake it with CSS)
EDIT: And after reading your text more carefully I think that what you try to accomplish is not possible. You want html textarea input where you can change some of the text to use different font and/or background color? I think that may be impossible since html textarea does not allow that. If it would be enough to change the style of the whole text then you would naturally apply the changes to the whole input (with style or class attribute). So I would stick with outputText and use CSS. Naturally there is something that does this in some third party JSF library somewhere but if you have already looked through richfaces and found none then I wouldn't try to include some second library if this is the only thing you need from it....