It has been requested before to make it possible to use a separate skin for admin pages and we may do it at some point. However, when I say Admin pages I mean pages under the admin menu. PageSettings.aspx and PageLayout.aspx especially should use the skin of the current page that they are editing.
In the case of PageLayout.aspx it must do so because the skin for the page may be using 5 content panes and the default skin or admin skin may not, but in order to use those extra content sections they must be present so one must use the page skin there.
Similarly for PageSettings.aspx, that is where you choose the skin for the page, if we don't use the page specific skin there then it will be a bug report saying that I changed the skin but it did not change it when I saved the page. It should use the skin that the user chooses there for the page so that it is obvious when the skin is changed.
Best,
Joe