Colt, like other factories, not only used hard wheels, but used shaped wheels. For example, a wheel might be shaped to exactly match the contour of the bottom of a revolver, trigger guard and all. That way, it was necessary to make only one pass to polish that entire area.
For a shinier finish, a gun could be polished on a smaller wheel with very fine grit, or even on a linen wheel with only a fine powder. But a high polish does not always add up to a blue (instead of black) color. In fact, the opposite is true because the blue color comes from light diffraction in very fine "scratch" marks. With just the right grit, you get a nice blue color; with finer grit, the color tends towards black.
I strongly recommend that anyone doing hot tank bluing experiment with different grits and different polishing techniques on scrap material before starting on a gun. There is a learning curve and it is a steep one.