The blue glow was not as thick on the Luke training scenes to begin with. If you look at those Technicolor frames, you'll notice that it definitely has more white core and less blue glow in that scene, vs. the other scenes with the lightsaber. Boosting could well have diminished the blue in that one scene only.
I just don't think the versions seen in the pre-SE home releases were altered to make it white. But I would buy that maybe they did something like that for the SE...