Dark Prussian Blue and Andrea Blue are a good start. If you want the very dark coat that most purists agree was the norm then you might want to start with the dark Prussian with a touch of black for a basecoat, then straight Dark Prussian Blue, then mix in a bit of Andrea Blue for highlights. Personally, I just start with Dark Prussian as a base, go to straight Prussian Blue for a mid-tone and mix a bit of Andrea in with it for highlights.