Innovative:republishing did not fix it
I just checked my stock calendar screen and all my past/future activities are all showing the correct colours. I also added a bunch of news ones and none of them seem to have any issue with the colour.
Are new items not changing colours or are past ones not changing? If you can give a little more detail around the problem I can try to recreate it and let my team know. We worked through this issue in the past and the there was an issue with the calendar object and the colour field on step 5 of 8. You may want to review the previous fix and see if anything changed here.
~C