The Yaucht's windows appear as purple and black boxes for me and I have the Counter Strike Source, the content downloaded for HL2 episodes 1 and 2, and the HL2 content.  I do not know what is wrong at this point.  I have verified the CSS files to make sure they are not corrupt and I do not know what else to do.  I checked with singleplayer and all of the yacht's textures work completely normal but when I go onto the HRP server, the yacht's textures (specifically the windows, glass-like textures, and some rectangular shapes on the wooden deck) only show as checkered.  The rest of the yacht is fine.  I have re-installed Gmod and re-installed all of my addon content as well as the server content.

P.S. One of the icons in the vehicle salesman's menu is checkered.     

here are some screenshots of the yacht for reference:
http://steamcommunity.com/sharedfiles/filedetails/?id=262233218
http://steamcommunity.com/sharedfiles/filedetails/?id=262233206
http://steamcommunity.com/sharedfiles/filedetails/?id=262233196
http://steamcommunity.com/sharedfiles/filedetails/?id=262233176
http://steamcommunity.com/sharedfiles/filedetails/?id=262233161
http://steamcommunity.com/sharedfiles/filedetails/?id=262233148
I hope this helps!