The named color renaming scheme (renaming things such as #FF0000 to red and white to #fff) is a tad too agressive, as it renames occurences everywheren.

In my particular case, it changes url(assets/images/white.png) into url(assets/images/#fff.png), which results in a 404. I suppose the regular expression attempting to rename these colors could be tweaked so that it only works on things that are actually colors, but I'm not sure how.

In the meantime, I'm working around this bug by renaming my file.