The first VC10K2, ZA141, was originally painted in grey/green camouflage with a light grey underside. We described this on US flight plans as 'lizard', hence '141 became known as 'The Lizard'.
Then they were all painted in hemp, with light grey undersurfaces. Which looked rather better than 'lizard'.
But when the RN started retiring many of its war canoes, a surplus of 'paint, grey, ships for the painting of' became available, so 'John Major Grey' became the colour of choice as 'Pusser' had oceans of the wretched stuff available to sell to the RAF!
The first grey VC10K appeared with a 'wedgewood blue' cheat line and white lettering, which received many ribald remarks about the 'blue vein'. Latterly the blue was changed to dark grey, as was the white lettering. Much tidier!