More likely I think, that Gresley RBs are being confused with the two Thompsons (1705/06, built for the 1948 'Flying Scotsman rake, AFAIK), which did work on ScR internal services until the mid/late 70s
The 1972 RCTS book lists 9115/22/23/24/28/29/31/32/35/95 (all E-prefix apart from '35, which was W); all would have likely been blue/grey by then, apart possibly from '95 which was a different design and withdrawn soon after.