Right, Randall. The only place I've ever seen the factory ID these cars as 3A models is in later editions of the Spare Parts Catalogue, where the cover was amended to read TR 2-3-3A models.
As for the change from red/black to blue/white badges, I'm pretty sure it was some time around the late summer or early fall of 1958, more or less for the 1959 model year. It happened company-wide, as the same change was made for the Triumph 10 badge as well as Standard 10, Pennant and other models.