Okay, but at 50% speed it should have a bigger change in colour.
And in all honesty, it looks like its printing just as fast as the upper layers.
When I print with a raft, it is ALOT slower.
Shoudn't the first layer of the skirt print, and the raft print at the same speed?
I think the speed difference you are seeing there is the "Support Structure Underspeed" set at 80%
Anyways, I'm playing with the z axis offset like you recommened. Hopefully it helps.