some info here:
they say:
Prussian blue
Cobalt blue
Ultramarine blue
“Ingres’ palette, however, was very much the same as David’s with the addition of cobalt blue and the new artificial ultramarine,”
the other blue that David used was prussian according to this source. I believe that these were in general, the primary blues used in that period.
It all depends what color you used to tone the surface if its a warm color like umber or burnt sienna
then it’s really easy to get a bright blue even ivory black mixed with white can make a good blue, the relationships with the colors is what makes 1 brighter than the other