There's a photo in, I think, one of the It's all books in either 48 or 49 of her in wartime black with 46221 on the cab sides.
I do quite like them in wartime black too. 6252 lasted to BR in plain black too, a loco I modelled in that condition some years ago.
Regarding the Princesses in LMS livery in BR days, 6204 did last until 1952 in Crimson Lake with BR number/LMS on tender.