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 app 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 app 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).
"I can't change the color of the button text when I hover over the button. Right now, the button text color is black so it becomes invisible when I hover over the button."
There's unfortunately no way to disable the hover effect on the button. You will need to lower the button's background color transparency for the button text to be visible when you hover over it:
There is no other workaround for this at this time.