I'm with @chrisb on this, 0.19.1 exports and imports colours fine. I also brought a STEP file that I exported with colours on certain faces from 2017 and it worked as expected.
The thing that stood out to me looking at the bug report is the reporter had both 0.18.x and 0.19.1 open together and therefore highly likely to be using the same config files. This is a big no-no now that so much has changed between the versions, I've even started with a set of 0.20 config files so I know for certain there's no 'pollution' across when I'm opening old files in the version they were built with.
OS: Windows 7 Version 6.1 (Build 7601: SP 1)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24276 (Git)
Build type: Release
Python version: 3.8.6+
Qt version: 5.15.1
Coin version: 4.0.1
OCC version: 7.5.0
Locale: English/United Kingdom (en_GB)