HMS Ganges August 8, 1826 leaving Spithead (Watercolour - item number PAD6126) NMM

In 1805, after the battle of Trafalgar, the rank of Admiral of the Red was introduced.
It became the highest rank that an Admiral could attain until 1862, when an allowance was made for more than one Admiral of the Fleet to be appointed. In 1864 the colour squadron organisation was abolished and the Royal Navy adopted the White Ensign of the former White Squadron. Therefore would assume the red ensign was in use at Salt Spring Island times of Ganges!
The White Ensign became the official standard of the Royal Navy and is still used by Royal Navy ships and shore establishments.

The Red Ensign of the Red Squadron became the ensign of the British Merchant Navy, and the Blue Ensign of the Blue Squadron became the ensign of the Auxiliary Fleet.