This stamp was issued in March 1855; it featured the portrait HRH Prince Albert of value 6 Penny. It was printed on a wove paper. Around 250,000 stamps were issued in the shades of slate grey, brownish grey and greenish grey. The portrait was designed by William Drummond Esq, the reddish-purple HRH Prince Albert 6 penny stamp was sold for 42,500 dollars at Spink New York in 2014.
Image Courtesy: www.arpinphilately.com