Nothing to do with nostalgia. Simply attractive colours.
Obviously GWR disagree with you.
LNER never used Caledonian Blue anyway.
My issue with red is simply that it's an aggressive colour, as is black.
It seems to me that the interior of a CrossCountry HST or a Transpennine 185, all other factors being equal, is a more relaxing environment - not because I particularly like burgundy or chalky blue, but because they are tones that don't set my teeth on edge.
There are enough other irritants associated with public transport without aesthetic environments adding to the stress, purely at the whim of marketing and branding.
I also, again personally, dislike the Azuma moniker, and the general level of reported (and experienced) staff disaffection with Virgin Trains East Coast management prior to June suggests to me that its persistent presence is again a marketing preoccupation, rather than some reflection of it being staff-chosen.
However, on the occasions when I have seen 'LONDON NORTH EASTERN RAILWAY' in its full, non-acronymised version on signage and advertising it looks powerful and authoritative (to use words that marketing folks like).
I would therefore lose the Azuma branding completely, but perhaps run 'LONDON NORTH EASTERN RAILWAY' along each carriage side, taking up the centre third of the available space, so maybe about 6 or 7 metres in length.