The following applies to all Gallery and Social Feed apps.
The Caption Description option shows in a color opposite to the one set in your App Dashboard when your plugin is set to appear On Hover. So if you have your Display Caption option set On Hover and Caption Description on blue, the description on the plugin itself will appear in the color opposite to blue (orange).
This is not a bug, it is merely a feature of Gallery and Social Feed apps.
Also, please know that if you switch the Display Caption option back to Below Media, the color of the description will be blue (as it appears in the settings).