When Great Western Trains won the first Great Western franchise, their design team considered applying traditional chocolate and cream colours to their HSTs, but apparently it wouldn't work, so the dark green and ivory scheme that was actually applied was chosen instead. The first class carriages were intended to have a mauve colour replacing the dark green areas, but this too was decided against.(IMO trains from Padd to the West should be traditional GWR Chocolate and Cream)
When Great Western Trains won the first Great Western franchise, their design team considered applying traditional chocolate and cream colours to their HSTs, but apparently it wouldn't work, so the dark green and ivory scheme that was actually applied was chosen instead. The first class carriages were intended to have a mauve colour replacing the dark green areas, but this too was decided against.
I'd quite like to see a variant of GWT livery brought back as a standard livery for the Intercity component of the Great Western franchise. But with less white/ivory.
Another which occurs to me - the Northern Spirit + First + Central Trains + Cross Country all on top of each other mess that some 158s wear.

I also disliked the Inter-City livery in the late 1970s-1980s which was two tone brown and orange, I understand that was sometimes called "Jaffa Cake" I think some trains in the SR & Gatwick Express also had that for a while.
Jaffa cake livery was similar but brown and orange and arrived in the late 1980s on London & South East before the sector was re-named NSE. A few CIGs, CEPs and MLVs only received the livery.

I think that the original NX Scotrail Livery was actually pretty good, especially compared to the Barbie blue rubbish that replaced it.
I actually really like the new Scotrail livery, particularly after I rode on 170434 last Thursday on the last train from Glasgow Queen Street.
On some trains I also feel that the SPT livery is pretty awful, some suit it but most that are/were in the SPT livery look horrid.
NXEC and the EC livery, both horrid liveries, the GNER dark blue with red stripe was a far better Livery.
XC is an awful livery too as is the Virgin livery.
As RyanB says, I don't think that the Strathclyde PTE carmine & cream livery suits any of the more modern unit designs: The use of the light blue stripe in an attempt to modernise the scheme really didn't work, but at least the traditional livery suited the 156s.
Yeah, Sealink was a very pleasing scheme to my eyes.Talking of Scotland, another favourite was the Mk1s that were painted in Sealink "livery" (though why they called it that I don't know, since it was nothing like anything ever seen on any Sealink Ship) in the '80's
* Also seen on an NIR DEMU, I find.
Connex
Connex
Another two:
Railtracks Lime Green & Blue - Which didnt look too bad on some locos & stock, but really didnt suit the meccano sides of 31190!
Railtracks Fake tan, white & grey!
http://carlswatson.com/Trains/Galle.../class205977939stleonards15thoctober2011.html
Though at least on that version, they didnt add any swoping curves or fancy lines!
As for Connex, i think it was one of those liverys that looks alright at the time - and only on certain units!, But give it time and plenty of weathering, and then it started to look sh*te and shabby! Though i prefer the version as worn by the Cigs & Veps, to the version on the 365/465s with the blue band along the windows!
Looks like it spent too long in the sun...Railtracks Fake tan, white & grey!
http://carlswatson.com/Trains/Galle.../class205977939stleonards15thoctober2011.html
Though at least on that version, they didnt add any swoping curves or fancy lines!
I think I'm actually alone in that I didn't mind the One livery...
I didn't like the Wessex Trains livery that advertised local lines/attractions - particularly as it meant that certain stock had to be on certain lines otherwise it looked even worse (ie the 'Heart of Wessex' line 153 on the Gunnislake branch...). I think their Alphaline livery would've suited the rest of their stock (minus the giant alpha symbol though). I also disliked the 143s or 142s (forget which) that got sent Devonwards which had the giant star at the front of them..