virtualbox.org

I have the following configuration:
OS host: MX Linux 19.4
VB: 6.1.14_Debian r140239
After install, the background color is white (please see the attached pic), and character displayed is almost white, how can I change it?

You are not using an official release of VirtualBox. You need to ask on the Ubuntu forums about any changes made when they rebuilt using the open sources.