The 8 colours are the defaults for ncurses. Support for any more would depend on the terminfo of your TERM.
USES= compiler:c++14-lang gnome iconv libtool localbase ncurses \
pkgconfig readline tar:bzip2
CONFIGURE_ENV= BOOST_LIB_SUFFIX="" ncursesw_CFLAGS="-L${NCURSESLIB}" ncursesw_LIBS="-lncursesw"
USES= compiler:c++14-lang gnome iconv libtool localbase ncurses:port \
pkgconfig readline tar:bzip2
CONFIGURE_ENV= BOOST_LIB_SUFFIX=""