Great experiment!
In reversal process, color development should carried to completion, meaning all remaining silver halide is fully developed. The push/pull, color shift, and contrast primarily depend on the amount of silver halide LEFT after the first developer. Therefore, the first developer...
I experienced a similar magenta cast with the same process on Aerocolor film.
Since the color development in the reversal process is to-complete, I believe the issue stems from the first developer not developing the three layers evenly.
I also noticed a slight magenta cast on Ektachrome 100D...
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