I am trying to use attribute driven symbology to define the colours of bus routes in a GTFS in ArcGIS Pro. The data contains a field of hex values without the '#' in front of the value (ie 007F5A) which doesn't work with setting colour properties in attribute driven symbology (I made a copy of the dataset and calculated a new field adding a '#' in front of the hex values and it worked so I know I am doing the correct process).
I am looking for ways I can get this to work without editing the dataset (as I don't have permissions) or copying the dataset into my own database (as it will be updated weekly).
In the set attribute mapping dialog where you select which field you want the colour to be based on there is an expression option which I was hoping I could use to add the '#' but it is greyed out and I have no idea why. I have tested on multiple datasets and it remains greyed out for all of them.
Is there any other way i could get this to work?