Files Greyed out in Finder - Potential extended attributes issue?
This worked, but after external disk (NTFS) eject the problem was back

xattr -d com.apple.FinderInfo fileToUpdate 


(or for all files in a folder xattr -d com.apple.FinderInfo *)

This worked after eject/re-mount

xattr -wx com.apple.FinderInfo 

0000000000000000001000000000000000000000000000000000000000000000 fileToUpdate


Notes from man xattr:

 xattr -w [-rsx] attr_name attr_value file ...
 xattr -x  Force the attribute value to be displayed in the hexadecimal representation.