Hello PlantUML team,
Here are some complements and test about Gantt, printscale weekly, coloring current week:
If we add closed days, as:
sunday are closed
saturday are closed
Case 1:
2020/10/26 to 2020/11/01 are colored in salmon
With daily printscale, this is OK:

But with weekly printscale, that is KO (We observe a shift of color on the last week):

Case 2:
2021-01-18 to 2021-01-22 are colored in palegreen
With daily printscale, this is OK:

But with weekly printscale, that is KO (We observe nothing... no palegreen color... just closed color...):

Thanks for your support,
Regards,
Th.