From 1940 onwards Bestall only coloured the cover paintings for the annuals. In order to produce full colour illustrations for the annuals the initial black and white drawings were photographed as pale blue keylines which were then hand coloured with watercolour usually by principal artist Doris Campbell. An overlay of the original drawing in black line were then applied over the top of the hand-painted colour. The overlays were produced by tracing the originals onto glass (later acetate film) and the underlay onto Whatman board.