That's a good question. In the 1990s, most US (and international too) airlines went through a major livery overhaul.

United of course went from the white with cheatline (line/s down the window line) to the cheatline-less grey and blue. Both new and old seen here. My favorite: New.

US Airways went from the metal with blue-and-red-accent cheatline to the cheatline-less shade of blue. Old /New
My favorite: New.

Air Canada dumped the cheatline and introduced a bare-body with block titles and a textured logo. Old/New
My favorite: New.

Canadian is another with three liveries. They have an old one, a new one (the goose logo), and the hybrid Canadian/Air Canda. Old/Goose/[url="http://www.airliners.net/open.file?id=127496"]Hybrid[/ url]
Favorite: Goose.

TWA had an old old one too, but finally introduced a really neat IMO one. Old/New
My favorite: New.

Both Continental and Northwest introduced new liveries in the early 1990s.

As far as the oldest US airline, I'd have to go with American. Or maybe even Southwest. They're the only ones in the US who haven't tinkered with their livery since the 70s or prior.

There are a couple of airlines that have three liveries, and this makes them fun to "spot" in airports. Delta has three, as described before. Canadian also has three. British Airways technically has three. They have their old black-bottom/white-top, the World Colors, and the Union Jack world colors, previously exclusive to the Concorde.

(edited for UBB errors)

[This message has been edited by BizJet (edited 12-17-2000).]