°thiefthis is a bunch of skyboxes I've found on the 'net and converted to be used in Thief. if you use NewDark, you need to extract the files to yourmodfolder\FAM\skyhw (yourmodfolder being the folder you've set up to load mods. after using TFix, this would be USERMODS. the "daybright" sky is already part of TFix).
the files can also be used with a DDFixed install of Thief, but the overrides are not included, so you will have to create them yourself, should you want to keep using DDFix for some odd reason (DDFix is considered deprecated and its use is discouraged).