Notice: The Animation tab is created for the first-generation layouts (“Grid” to “One and others”).
For next-generation layouts (“Grid 2” to “Big Post 2”), the Animation tab is disabled. Instead, you can use Overlay 1 to 8 to have the overlay feature with more powerful options.
In Animation tab, please select option “On hover” for the “Overlay Thumbnail With Text” setting.
To change text color and background color of the overlay, please use Thumbnail Overlay setting in Style Settings tab:
To change the opacity of background color, please check this document.