Done! Thank you, @MrMiyagi!!

Yup! Subscribe to your own item (lol I know, I know). Make a file called PreviewImage.png, maximum of 800x450 pixels, then go back into the game and at the main menu select Content Manager, then you'll see your item's version with the steam logo next to it and a button "update". Click that, then click the TINY manila folder on the lower right (like this image here http://www.skylineswiki.com/File:Gif_save_asset_picture.gif ), a Windows folder window will open, overwrite the existing PreveiwImage there with your custom one by copy paste, but do NOT close that file window until the file is updated completely to the WS

Does anyone know how I can create a thumbnail / preview image for my LUT? :)

Less yellow and super dark shadows? SOLD!

@Mercenary - it absolutely is!

This is AD compatible?