Why would you think that a fidelity to lore applies in this case in particular, when it has been ignored in so many others?
In the Alatar/Palallando iteration of the Blue Wizards, it is Oromë who chooses Alatar, and he brings Pallando as a friend. This is the version that places Curunir as a Maia of Aulë.
In the Morinehtar and Rómestámo iteration of the Blue Wizards, which brings them with Glorfindel to Middle-Earth around SA 1600, no particular Vala is associated with their mission.
Saruman's staff in the movie is designed to evoke Orthanc, and while the show draws heavily on the movies, I don't think it's completely bound by their symbols.
Given that the show can't use any of the names associated with the Blue Wizards - and maybe even the term "Blue Wizard" - because they don't have the rights, I suspect it will be Saruman.
Besides, 'member Saruman? Either that, or they'll just leave him as "The Dark Wizard" or choose some other name.