Vincent,
Sorry I don't have time right now to find any precise web addresses, as chores are awaiting my tardy attention.
Two quick hints:
1/ You might find examples of your desired wikitext by clicking on the edit tab of any unlocked profile that uses the attribute(s) you would like to use.
2/ All recent versions of OpenOffice can export to wikitext. Compose a document in OpenOffice using whatever attributes you want (font size, color, etc.), save the file as a document, export to wikitext, open the wikitest file in notepad, then cut and past the wikitext into your WikiTree profile or category page.
Updated 07/04/2014: Thank you Denis Barton for identifying my oversight in not mentioning an Apache Open Office Extension called Sun Wiki Publisher is required.