When pulling from a report to create a calendar the column type needs to be a dropdown to assign custom colors. When pulling from a sheet it doesn't have to be a dropdown. This is not documented anywhere. Please make it so what you can do with custom colors in a calendar from a sheet can also be done with a report.
I highly agree! I just came across with this issue and I was puzzled why. I would love to use custom color by column Calendar app created FROM REPORT also. We have so many projects provisioned by Control center and there is no easier way to create the calendar app without using the report. This would be very handy to have. Thank you.