It appears as thought the device registration problems might be associated with the beta build. I reinstalled from the play store and had no problems registering the device.
I then reinstalled the beta apk, but couldn’t register, so I’ve reverted back to the play store app and it registered without problems.
I can confirm that the icon is now white in the top status bar, so it displays nicely on the default coloured home page, and also the default orange colour of the openhab app