I catagorize French Ultramarine Blue as an Almost Transparent color. It can make wonderful glazes when oily enough or can cover in an opaque manner straight from the tube if not so oily. I relied heavily on this color in my early years of portrait painting for cooling colors in the shadows of the face and I would place a pure dot of it into the iris of the eye instead of using black, which would go flat and lifeless in the eye. I have now added Phthalo Green (WHO COMES UP WITH THESE NAMES?) to my color box and use it almost exclusively for portrait work in place of French Ultramarine Blue. (But not in the eye!) Thank you to Portrait Artist Edward Reed (Ted) for showing me this wonderful green.
Back to Blue now.....French Ultramarine Blue is a must have for landscape painting. An infinite number of greens can be made with it and no northern plains sky would be complete without it. Remember I said that mixing Cadmium Red with Blue would not produce a good purple....well it will make a great muddy purple or lavendar if mixed with French Ultramarine Blue and this color mix would look just fine in a landscape painting, especially a nocturnal scene. NOW, LETS GO PAINT!