[kube]

You could try these, I think 4.1.8 does the same...

locate the following in skin1/skin1.css for Product page thumbnail image...
.PImgBox { /*and add/change the border here*/ }
or if it fails add to CSS with...
.PImgBox IMG { border: 5px solid #FF0000; /* a test red border direct to IMG */ }

the same for Categories page thumbnail images, locate in skin1.css ...
.PListImgBox { /*and add/change the border here*/ }
or add directly to img in CSS with...
.PListImgBox IMG { border: 5px solid #FF0000; /* a test red border direct to IMG */ }