Auction 333-341 Western Australia & Great Britain - Day 3

1898: 2 d. blue registered stationery envelope, uprated with 1887 ½ d. vermilion, ½ d. dull blue-green and 9 d.dull purple & blue, sent from London to Darmstadt, Germany, dated 11 December 1900, tied by registered oval in black. To the reverse two arrival circular datestamps in black (12 December 1900). A very rare mixed franking combination of the two colours of the Jubilee ½ d. Additionally, comes with a cover franked with a combination of a single 1887 ½ d. vermillion and four 1900 ½ d. dull blue-greens sent from London to Bruges, dated 3 April 1901. Is soiled but a scarce cover and rare duo (2). 
Note: The change of colour of the Jubilee ½ d. to green occurred with effect from 17 April 1900. Post Offices were required to exhaust their stocks of the predecessor ½ d. vermilion before issuing its replacement, greatly limiting opportunities for the two stamps to be used together. Mixed frankings of the two stamps are rare, especially on commercial covers - this is the only recorded example.
Reference: Great Britain Victorian Mixed Franking Covers, by Ray Simpson & Karl Louis, first cover illustrated on pg. 241. Gold Standard cover.