I too witnessed this (Flt Cdr on 98 IOT). Watching a jet pull up to clear the trees over the sports pitches between Whittle Hall and CHOM was a clear indicator of what was to come - caps, marker poles, blue blankets everywhere!
I seem to remember it added to the fun because the blue blankets were wet and the dye had run into a number of lady's dresses.
Tell em that today an ............