[NTG-context] number of chapters

Hi, how do I access the current chapter number and the number of chapters (including appendixes; after the first run)? I’d like to setup a chapter color like \definecolor[ChapterColor][ s=1,v=1, h=360*\namedstructurevariable{chapter}{number}/\numberofchapters, ] and use it for a thumb index... (I can’t access the wiki ATM; downforeveryoneorjustme.com says it would be just me.) Hraban