I am not sure whether the use of white stripes on the BR blue livery was an early continuation of this practice before the full stipulations of BR’s new corporate identity were fully enforced: This certainly seems probable with the Hymeks when they received white window surrounds with small yellow warning panels, before the all-over yellow fronts and cab window wrap rounds were adopted as standard. It seems that the application of white stripes on the BR blue livery was more of an unofficial practice carried out by particular depots – Such as Finsbury Park’s white window “Deltics” and Stratford’s silver/grey painted roofs.
I've done some back-reading now and my recollections seem fairly accurate. Certainly in the case of the Hymeks with white window surrounds, Swindon decided to go ahead with their repainting before they had received the official livery drawings. No doubt this also occured at other depots on other regions, too.
Beyond this, the application of various "white bits" does seem to have been at least semi-unofficial based on a particular depots' preference: As mentioned previously, Eastfield were quick to apply white stripes to their 27s and 37s, as well as to a visiting class 44 that turned up once for an open day!
The Newton Heath based class 104s received white waist bands in an attempt to publicise the improved service provided by the Manchester Victoria to Blackpool "fast" services (Though I have difficulty in envisaging a service worked by 104s as being claimed to be "improved"!), and Buxton based DMUs began to receive white cab roofs in 1984: I wonder if this latter treatment also might have had a practical application in reducing the temperature in the cab during the hot summer months?
