Great Britain 1840 1d Rainbow colour trial (State 2), SGDP20aGreat Britain 1840 1d Rainbow colour trial (State 2), SG DP20a. A very fine unused bottom marginal example printed in lilac pink on white wove paper dipped in prussiate of potash. It has long been believed that the voiding of the corner letters in these Rainbow colour trials was achieved by filling the grooves of the printing plate with wax. Recent research has brought this view into doubt as it is considered to be highly unlikely that the wax would