Had absolutely no idea until you mentioned it.

Certainly an interesting chain of events at any rate!
31255 does ring a distant bell in regards to being used as a testbed of some description for a new paintshop (no idea what it was called) at Toton, though am sure someone with the correct info will set us both straight. What I am fairly certain of however is that 255 didn't see any front-line service after repainting, while 466 was one of the last 31s in service with EWS when they finally dispensed with the type's services in early 2001.
Now that you mention it, 33030 was repainted at Allerton T&RS Depot for the 1998 Toton Open Day as you say; it only saw a few months use in it's traditional area after this before all of EWS' remaining 33s were put into storage at the end of that year (linked images from the Doug Birmingham & Chris Morrison Flickr streams respectively).
The only Class 33 to appear in EWS livery was No 33030. See here inside Allerton T&RS Depot. after an excellent paint job carried out by the depot staff. Note the "8J" on the blinds which was Allerton Depot's former shed code in the latter days of steam before it change to "AN". The loco's first...
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Cromptons 33019 shorn of its 'Griffon' nameplates in faded 'Dutch' livery and 33030 in EWS livery head the Luton - Angerstein Wharf aggregates empties at Wandsworth Road in September 1998. Both locos were withdrawn in December 1998 and this was the last time I photographed them on the Southern...
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It would later be one of a pair of 33s that would be transferred to Aberdeen in September 1999 for use in/around the city (Civil Engineer's Dutch-liveried 33025 was the other one) on shunting, trip & infrastructure workings; maintenance was undertaken in Motherwell with the 2 locos hitching a ride to and fro on revenue freight workings to enable this (linked image from the Jim Ramsey Flickr stream). They didn't last too long in this role however, both having fallen out of use by the end of January 2001 (030 had caught fire at Kennethmont while at the head of the 6A11 Huntly - Aberdeen trip working on January 16th). Both would eventually leave Motherwell in February 2002 after being sold to DRS.
66197 with 33030 DIT are seen heading north through Carnoustie with 6A02 Mossend to Aberdeen Guild Street. The 33 was being taken back to Aberdeen for shunting/trip duties after maintenance at Motherwell.
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(Allocation info drawn from the superb derbysulzers site, link here)