The house flag of Green's Blackwall line (R. & H. Green & Co. Ltd). A rectangular white flag with a blue square in the centre and a red cross overall. The flag is made of wool bunting with a linen hoist and is hand sewn. It has a bolt-rope in the hoist, eye-spliced at the top. This design was introduced in 1843 when the Blackwall shipbuilding and shipowning firm of Wigram & Green split in two. While Green's from that point put the red cross over the blue square, Wigram's kept the old joint house flag (from 1824), which had the blue square over the cross, and from 1896 that version became the house flag of their successors, the Federal Steam Navigation Co.

The Green and Wigram families were in partnership from 1805 as shipbuilders and later owners, based at Blackwall on the Thames. The firm had an early history of building East Indiamen and after 1837 the new Green design became known as Blackwall frigates. In 1843, the partnership was dissolved and the shipyard physically divided. The Green offshoot became known as R. & H. Green under this house flag. In response to the Australian gold rush Green's extended their routes from India to Australia. By this time they were also building clippers. The last of their fleet, 'Carlisle Castle', had been sold by 1890.