GitHub Wiki allows for many benefits, especially for documentations, release information, and much much more! Categories in GitHub Wikis are best defined as the sidebar; given its name, the sidebar appears on the right-side of a GitHub Wiki and can be customly formatted via Markdown. For templates (regarding the physical attributes of a wiki page), I have not seen any templates that can be added that will physically change the appearance of a wiki page; not sure if GitHub officially supports wiki templates in the first place. For changing text color, wiki pages can only use the standard font and color that are provided with the page; no custom fonts or text colors can be added to change the pages appearance. Hope this helps!