This might be of help in addressing the problem with Ambiance GTK theme: apparently, only the outlines are displayed in their colour, not the filling, cf. this pull request conversation over at numix-icon-theme: https://github.com/numixproject/numix-icon-theme/pull/303
This might be of help in addressing the problem with Ambiance GTK theme: apparently, only the outlines are displayed in their colour, not the filling, cf. this pull request conversation over at numix-icon-theme: https:/ /github. com/numixprojec t/numix- icon-theme/ pull/303