I've just watched the video again, and unless it has been doctored in some way the nameplates are different. If you want to watch the video is is called "Saturday 12 March 2011 70013 Oliver Cromwell" posted by 447CDH with about 602viewings. It not worth
loosing sleep over, but I'm sure the plates are different colours.
As I said to PP, there is a video on Youtube taken in March 2011, which starts with a couple of coloured stills taken from both sides
of the loco showing the nameplate, one is red, no doubt, but even allowing for sunlight etc., I would say the otherside is black. So if there were two different coloured nameplates, which I'm sure there are not, it would be a very recent development.
I will check my Brit books re the Cromwell colours but some locos had black background plates and some had red at various times. I am not sure if Cromwell carried a mix in the 60's but may have in preservation at some point.