Use case

The motivation is here, I came across it today as well.

The solution here says to create custom transitions, this is an overkill to me.
#115995

The solution here suggests removing the transition altogether which is is not a real solution, but was accepted for some reason. With the conclusion: "The conclusion seems to be: do not use the default transition or you will have issues." That is something I do not want to be a conclusion about Flutter :D
https://stackoverflow.com/questions/74978431/black-border-around-scaffold-body-during-page-transition

Proposal

Currently the _drawScrim in _ZoomEnterTransitionPainter hard-codes

Paint()..color = Colors.black.withOpacity(scrimOpacity),

Instead, a Color? scrimColor could be passed in and default to Colors.black if none was set.

I have examples (slowed down 8x)

Current example: (produces weird black bars on the edges, looks worse at full animation speed)

With simple change of:

Paint()..color = Colors.white.withOpacity(scrimOpacity),

I can get rid of them.

So the proposal is to make the color a parameter that can be passed in.
I am willing to do it if this proposal is accepted.