If I understand this correctly it seems there is a bug where the default fill background pen affects the fill for schedules in layouts - why I don't know.
Go to your plan and look at the default setting for the fill background pen.
If it shows as a coloured wheel then this is the problem change it to a valid pen colour - probably the transparent pen (pen 0).
Then update the schedules on your layouts.
One of the forum moderators. Versions 6.5 to 25 Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10 Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10