This was not a Latin-specific trend, but a general typesetting trend in early modern Europe. For example, Robert Boyle's Experiments, Notes, &c About the Mechanical Origine or Production of divers particular qualities (1675) has a similar format:
As does Hauksbee's Physico-Mechanical Experiments on Various Subjects (1709):
French titles used this style as well, for instance the Journal des Voyages de Monsieur de Monconys (1677):
It was dependent on the printer and the location. Looking at Italy, the Saggi (essays) of the Accademia del Cimento (1666) used different colors and less variation in font:
I'm not sure if there was a convention for this sort of typesetting, but it was common and "trendy" at the time. It's not Latin-specific though, so you'd probably do better to ask this on the History SE.