Well, i have recently installed a mod called unique imperial textures which makes it possible to give castles textures different from the res.
However, i did not DL textures yet, so theyre just white. If you have any suggestions, please post a link to a *high quality* texture replacer together with the name of the Castle replaced. Id be very happy for your suggestions. =)

These are the available castles. Correct me if there are more, id love to have this for Solstheim.
Buckmoth
Ebonheart
Moonmoth
Pelagiad Caste
Tel Vos
Wolverine Hall

you german? look http://forum.worldofplayers.de/forum/showpost.php?p=12741779&postcount=11.

uh there some nice ones. especially like the blue roofs. ty!
keep em coming, i need inspiration. =)

the blue roofs are scorcha ravenlock the white walls (and interior) is from blm. i mostly use two diffent replacer on each castle except for buckmoth who has the original dark stone texture.

and i think i listed all imperial replacer i could find, so there shouldn't be that many more. i searched quite hard for those mentioned in that thread.