Re: The pigment and the hue
The first thing is that the pigment (Cobalt Blue, PB28) is always going to be the same chemical, cobalt aluminum oxide, and have the same pigment number, PB28. It may be marketed under different color names and the color may vary slightly depending on the paint formulation by various manufacturers, but it will always be the same stuff.
A "hue" is a paint that is formulated to look like another pigment or color, but is not made of the same pigment. Usually a hue uses a less expensive or less toxic pigment, but in some cases it is made to replace a pigment which is no longer manufactured or has other issues. A "cobalt blue hue" may contain different pigments depending on the manufacturer, it will not be pigmented only with PB28, genuine cobalt blue pigment.
There is also "student grade" paint which may contain fillers or a lower pigment load if it is the genuine pigment, and many also be a hue.
"Let the paint be paint" --John Marin