Cobalt is the other blue on my palette. It is an expensive color, but is worth it's price for its cool, clear, sky blue color. Cobalt blue is a heavy metal color and is toxic, so reasonable cleanliness is important. Available since the early 1800's cobalt blue has long been a staple on the artists palette. The blue in Maxfield Parish's work is cobalt blue. Ultramarine is my warmer blue and cobalt my cooler blue. Sometimes, as I said before, I use really high key mixtures of white and viridian to make a blue that looks like cerulean.
Prussian blue is a very dark almost black, blue color. Prussian blue is a color that was supposedly impermanent, however the manufacturers mark it as permanent. I use it sometimes because it has a greenish cast that I like because it looks old timey. Prussian blue has been replaced today (except with me) by pthalocyanine which I find difficult to control.
Cerulean blue (cobalt stanate) is a light, delicate, opaque, slightly greenish blue. It has become very expensive in recent years and many makers only provide a hue which is, as usual, totally unsatisfactory. This is a great color in skies.
Manganese blue, was a permanent green-blue that was available when I was a student but was found to cause nervous system diseases. Now unavailable, I have heard its loss lamented many times by older artists.
Pthalocyanine blue, is a permanent, extremely intense, slightly greenish blue. It will tint to green or violet and is used in printing and industry besides by artists. I don't often use it as I find its pigmenting strength a drawback, being so much more powerful than everything else on my palette. However it makes great greens. If I had no viridian I would choose pthalo to build greens.
Most of the blues with names like azure blue or other evocative names are mixtures of pthalo and white. If you don't know what a blue that you see on a color makers list is, chances are reading the label will reveal it as a pthalo mixture. It is an inexpensive pigment and you could paint your whole house with about a quart if it was thinned properly.
Pthalo is used to make cerulean hue, viridian hue, cobalt blue hue, ocean blue, anteater blue, and just about every other "mystery blue". It is best to buy only named, single pigment colors, like cadmium red or ultramarine blue, rather than, hyacinth cerise deep or moonlight blue. The colormakers market dozens of these romantically named mixtures, mostly for the hobby market and students. If you like those colors you can mix them yourself on your palette and get more variation within that color yourself.