It's at the start of a new game. On the PS1, it displays the loading screen, while on the Saturn, they desaturate the RGB to make it appear black on the previous screen, whatever it may be. I believe it's the same throughout the game. We should check other loading screens during debugging.
So if that's really the case,
It would require significant programming to make the game buffer an image, but for every loading screen. It won't be easy.
Here is the file in memory, even during the black loading screen at the beginning. (It's simply the previous title screen.)TITLE.D
But it appears black because the colors, instead of starting from 0, start from -256. Therefore, no colors are displayed.
I could be wrong, but I believe this is the technique used throughout the game.