Outside of the Hoverbox beta or Rollover app, it IS possible to setup images in Wix that have a transparent rollover color to indicate that they are linked or open larger.
To add an image rollover effect to ANY image in Wix, just follow these easy steps:
Simply add an image to your Wix page in the editor
Click on the image to see the image menu icon options, and click on the Design paintbrush icon
In the Image Frame Design box, click on "Customize Design" at bottom
Choose the second layout example in this panel (the one with the cursor over it), this will give your image a rollover hover color – once you choose this design, you can then choose the color and transparency level in the Hover state of the image settings.
This is better than using the Rollover Image Effects app as I just wanted something subtle (a shift in color) to indicate that the image is linked. See screenshots below for details.