I cannot find any information about this attribute value. the attribute 'w:themeColor' is found in alot of elements like: "w:color" "w:shd" "w:bottom" etc.. and the attribute 'w:themeColor' can be set to any of the values defined by the Simple Type 'ST_ThemeColor'. In this simple type there are the regular 'accent1' ... 'hlink' etc... but they also have 'text1' 'text2'.
Where are these defined ? i know they arent defined in the "a:clrScheme" element inside the theme file because they are not documented at all.
In PresentationML, a "p:clrMap" is usually defined that has values for these extra theme colors. Where is this stuff set in WordML ?