Reproducing Step:

1. open zssapp
2. create a blank sheet
3. select A1, change its background to black
4. copy A1
5. select B1, select "paste special \ format"

Expected:
B1 becomes black background.

Actual:
B1 remains white background.

Extra:
3.0.1 doesn't have this issue. The "paste format" option will paste background to a cell.
Excel pastes cell style when pasting format.