The black will be a Primer, and it is not an uncommon maintenance task.
Nimrod '36 was painted in its trial Grey scheme from 1998 as part of the MRA 4 programme, I took her to Farnboro' that year
I digress
I have seen a pikky taken in the BA Paint shop at Heathrow,
36 was one of the last jets BA painted for the RAF and the aircraft was definately in Black Primer, it too looked pretty cool.
Not bad for the Funbus fleet though taking 7 years to catch up with the Kipper Fleet.