The biggest improvement of the color processing in ALEXA SUP 3.x is a better handling of out-of-gamut colors. Their mapping into the target color space is more gentle and smoother.
The images on the left side were generated by SUP 3.x. With increasing exposure the color patches in those images maintain more of their color as in the images on the right side, which were generated by SUP 2.x. The transition into over-exposure happens in a smoother way.