This one has a white top.
The Mk 1's were grey with a white top until the mid to late 70's. The white was to reflect heat, since there was rather a lot of heat generating electronics on board. They then came up with a coloured, matt paint which reflected heat, so it was planned that each aircraft would get camouflage paint next time it was due a re-paint. First one to be done emerged with a brown finish. The story at the time was that some storeman transposed two numbers in the Sect/Ref. code. All the rest were done in "Hemp", a greenish grey. The first one was known as the "Chocolate Bomber". It did not get a repaint until all the others had been done, and it was its turn again.
The 4's were indeed all over grey, but looking at photos, the top could look paler in bright light.