Many Drupal users had reported that Colorbox has a white flashing background when loading iframe content before reverting to the default black. If you are facing the same issue in Colorbox in your Drupal site then read on to find out the solution.
Iframe
A few Drupal users using the Embedded Media Field module had mentioned that they encountered an error while using Colorbox to open a video thumbnail embedded in a View. The Colorbox with the video iframe triggers another Colorbox with no content enlarging the previous Colorbox and causing a white vertical line to appear on the left side of the video and enlarging the parent Colorbox. If you are encountering the same error in your Drupal website then read on to find out the fix.