Gallery2 Module for Drupal - Random Image Block - gray layer/background

I have a random image block on the sidebar of my Drupal pages. This works well and I have not problem with it. However there is an annoying layer of gray beneath the two random images that I want to get rid of. (I want a white background.)

Yesterday I played with the gallery.css that comes with the module. I'm able to control the images, the borders, the background -- but I can't find where to control (what seems like) the layer below.

Is anybody able to help me with this? Using:

Drupal 6.11 - Module Gallery 6.x-1.0 and Gallery2.3

Thanks,
jdn