At least the first four sets were delivered in the darker 'Loco Green' shade of green, carring the 'lion on wheel' logo. The first image shows M50136 in this condition.
The second batch were delivered with the coaching roundels (and these were handed) and so would probably have started out in the lighter 'Multiple Unit' green.
By the time the 51xxx vehicles were delivered the darker 'Loco Green' would by then be again the standard, and all the vehicles would probably carry this by the yellow panel period.
The green lining followed the Met-Camm style having three lines instead of the regular two, although the two line style probably appeared after repaints.
Starting in 1965 the NER vehicles would start to carry the NE prefix.
I have seen no evidence of the vehicles carrying the short-lived early blue liveries with small yellow panels or yellow cab doors, so standard rail blue would be the next livery change.
After the 4-character route indicators fell out of use, sometimes these were painted yellow.
Their final livery was blue / grey, often with Metro-Train markings, and red buffer beams in this era was not unknown. The image shows 78972 at Keighley on the 10th August 1985 Bill Read.