Indexhibit Support

how can i choose overlay dark or white for each exhibit individual?

i meaned in visual index format

You'll need to customize the format to get this as an option for Visual index.

There's a quick-n-drty way though.
Set the overlay to Light, for example from Admin > Visual Index, Options.
Then for the exhibits that you want to be with a dark background insert in the text area

1. <style type='text/css'>.light-overlay { background-color: #000 !important; /* opacity: 0.9; */ }</style>

it works perfectly! thank you!!