Earth often seems to load random images instead of the ones specified in kml. For example load the kml sample from the kml documentation for IconStyle (https://developers.google.com/kml/documentation/kmlreference#iconstyle) It specifies the image at http://maps.google.com/mapfiles/kml/pal3/icon21.png which when viewed in a browser is a building on a green field, but in earth shows up as mountains.
Seems almost as though earth is hard coded to use an internal palette whenever a google hosted image is found and the palettes have gotten out of sync.
(Earth version is 6.2.1.6014 (beta))
I think this is a unfortunate legacy issue.
Google Maps at one point changed around their icons - reusing the same filenames!
Google Earth on the other hand knows that many users where using the specific icons in their Places and KML files. So rather than everybodies icons suddenly changing randomly, they choose to still show the old icons.
Would be funny if it wasn't true!
If you really want to use Google hosted icons, you could use an alternative URL - one that hopefully Google Earth wont attempt to 'fix', eg http://googleapis.com/mapfiles/kml/pal3/icon21.png
But really would not recommend relying on Google Hosted icons. They can change at any point.
