It was indeed duck-egg blue. My primary school was on the extended centre line of the Wisley (easterly) final approach path and the aircraft frequently flew overhead. Although only a nipper then I always took a keen interest as father was a BEA Viscount co-pilot at the time.
I also remember that there were a couple of Viscounts painted in the same colour "experimentally" and if I remember rightly one was later written off.
Sadly, the colour of the cheat line escapes me in the mists of time.