German Empire stamps overprinted "Danzig". The overprint colour of No. 41 is dark violet ultramarine and Nos. 42-43 are between dark red and dark pink. These stamps are known as the "großer Innendienst" (big office work) issues in Germany.
These stamps were not to be sold in public. The stamps were officially intended to be attached to mail by post office employees at the counter. However, most of the stamps were just sold.