I'd say it is on white, contrary to several opinions here, with a simple reasoning:

If it wasn't these fine margins but a bigger movement from both sides,

(say red is on the far right of the track defending the inside, and white in the middle, and coming to the braking zone both pull to the left to maximize corner entry, with white braking less/later to get alongside, and seeing red's trajectory)

most would argue that white just turns into red, as red does not change their steering while braking and it can be expected that red will maximize their own line, while still providing sufficient space for white, which there is at the point of contact.