The Penny Blue is from a series of proof impressions which were made at the time Rowland Hill was looking at the new colours which were to be used for the stamps which were to replace the Penny Black and the original 1840 issue of the Two pence Blue.
The decission to change the black stamp to red had already been made, and at the same time the colour of the ink used for the cancellations was to be changed from red to black. Although it had been decided that the two pence value would remain in blue, this was going to be printed using a diffrent ink from that used on the original. (Thus when the stamp was printed it had the addition of white lines added above and below the inscription so that the new printings could be distinguished at a glance).
At the begining of December 1840, Rowland Hill wished to ee what the stamps would look like in the new colours and requested, (in sheet form), examples in the red brown which was to be used for the new one penny stamp as well as two sheets in blue as the choice of colour had not yet been made. The two blues used for the printing were full deep blue and prussian blue.
For the printing of these three sheets, plate 8 constructed for the production of the penny blacks was used. The choice of plates was probably just one of convieniece as this plate was already on the presses being used.
Rowland Hill choose the full deep blue colour for the two pence stamp.
Some of the blue stamps made it onto postage but these are extreamlly rare. What became of the bulk of the 480 impression is unkown.
Examples printed in the red-brown shade, if they made it onto postage, would be indistinguishable from later printings which were made in this colour as part of the general issue in 1841.
