The panels at the top, bottom, left, and right in the Lightroom user interface become 'black' intermittently when you perform actions such as switching between Lightroom modules, or minimizing and maximizing the Lightroom window.
Issue: Panels appearing black in Lightroom
Product versions affected
Lightroom CC 2015.8/Lightroom 6.8 and earlier
macOS 10.12 (Sierra), Mac OS X 10.11 (El Capitan)
Lightroom team is actively investigating and working on fixing this intermittent issue of UI panels becoming black, and close to finding a solution. However, a fix is not yet available in the most current update of Lightroom. We are hoping to have it fixed in next update.
When the Lightroom panels appear as black on your Mac, follow the workaround steps given below to resolve this issue:
In the Dock bar on your Mac, right-click the Lightroom icon and select Hide from the menu.
Hide Lightroom using the Dock menu
Right-click the Lightroom icon in the Dock again and select Show from the menu.