Success! After experimenting with different solutions in my theme file without much luck, I decided to attempt the fix directly in the Colorbox library's folder (even though it felt like tampering with the core system).
Here's a tip for those who may encounter the same issue:
- Go to sites/all/libraries/colorbox/[insert your colorbox preset name here - mine was "example1"]/colorbox.css and make a copy of it.
- Rename the copied file to colorbox.css.bak
- Open the original colorbox.css
- Delete the specific lines located at the bottom of the file.
/*
The following fixes png-transparency for IE6.
It is also necessary for png-transparency in IE7 & IE8 to avoid 'black halos' with the fade transition
Since this method does not support CSS background-positioning, it is incompatible with CSS sprites.
Colorbox preloads navigation hover classes to account for this.
!! Important Note: AlphaImageLoader src paths are relative to the HTML document,
while regular CSS background images are relative to the CSS document.
*/
.cboxIE #cboxTopLeft{background:transparent; filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src=images/internet_explorer/borderTopLeft.png, sizingMethod='scale');}
.cboxIE #cboxTopCenter{background:transparent; filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src=images/internet_explorer/borderTopCenter.png, sizingMethod='scale');}
.cboxIE #cboxTopRight{background:transparent; filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src=images/internet_explorer/borderTopRight.png, sizingMethod='scale');}
.cboxIE #cboxBottomLeft{background:transparent; filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src=images/internet_explorer/borderBottomLeft.png, sizingMethod='scale');}
.cboxIE #cboxBottomCenter{background:transparent; filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src=images/internet_explorer/borderBottomCenter.png, sizingMethod='scale');}
.cboxIE #cboxBottomRight{background:transparent; filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src=images/internet_explorer/borderBottomRight.png, sizingMethod='scale');}
.cboxIE #cboxMiddleLeft{background:transparent; filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src=images/internet_explorer/borderMiddleLeft.png, sizingMethod='scale');}
.cboxIE #cboxMiddleRight{background:transparent; filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src=images/internet_explorer/borderMiddleRight.png, sizingMethod='scale');}
- Save your changes in colorbox.css and you're all set!