in the /gallery/galleries/grid_lightbox/css/themes/gallery.php?theme=Light2 file, change:
.pg-gl .thumbs img {
border: none;
border: solid 4px #v;
margin-bottom: 17px;
}
to:
.pg-gl .thumbs img {
border: none;
border: solid 4px #ffffff;
margin-bottom: 17px;
}