I read it in college but can’t remember enough to track it down. It involved a family of sorcerers and black and white magic cubes that when placed in a certain arrangement would enable the sorcerer to cast a spell. There was also a lot of anti-magic sentiment throughout the series and early on, the series dealt with the succession to the countries throne.
Katherine Kurtz’s Deryni series.
The black and white cubes are, IIRC, a minor plot in the Camber of Culdi series that I don’t recall ever getting solved.
Succession to the country’s throne carries throughout all the Deryni books, as does the anti-magic sentiment.