(a) An unique theme named 'XFE', for all the three sections (color, controls and icons). Probably a theme that is designed to follow generic FOX theme.
(b) Two variant's of 'XFE' theme, for all the three sections (color, controls and icons).. Light and Dark. 'XFE-Light' will have blackish texts with whiteish background. 'XFE-Dark' will have whiteish texts with blackish background.
(c) 'XFE-Light' as the default theme, for all the three sections (color, controls and icons).
(d) This idea is similar to how themes+apperance works in Firefox and Gajim. The theme can be switched between light and dark variants; based on day/night, lighting conditions, eye issues or preference.
(e) Other exsisting themes can still be maintained as options, if required.
(d) Consistency of applied theme between xfe, xfw, xfp and xfi.
You can customize Xfe appearance using Edit/Preferences/Appearance/Custom colors. Each Linux distribution has its own theme, and it changes over time. It's not posible to match them all.
The idea is not to match with any distro, but to have an independent and pre-defined theme. That is also consistent across Xfe, Xfw, Xfi and Xfp.