@gap - great idea with the test.
I just performed the test and indeed, only the first (top most) entries are applied when there are duplicates involved. There is no blending going on, the next entry is simply ignored.
SkyTopColor=FF000000 added first:
SkyTopColor=FF000000 added second:
With that out of the way now - I will proceed with the merging and when duplicates are found, I will use the top/first entry.