If this occurred following the 2004 update, then boot into the advanced boot options by pressing and holding SHIFT throughout a Restart.
Click on Troubleshoot/Advanced options and then on Uninstall Update.
The 2004 update will have been a feature update, so select that option.
I'm not sure if you have to give a reason why you want to uninstall it, but after uninstalling the update, check to see if your search bar has returned to white.
If it has then click on the Windows icon then on the Settings cog - double click on Update & Security and click on Check for updates where the 2004 update should re-present itself.
It may have been a bad install,
