In fact it turned out that there was no mysterious Colonel Hallows. The family story, which claimed Hallows was a Colonel in India, and left his wife and family well off following his death, was inaccurate although not without foundation.
Mary Elizabeth Hallows, 2nd great-grandmother to my first husband James A Andrew Baker, was the daughter of Thomas Hallows, a stone mason originally from Bakewell in Derbyshire, and Sophie Jenour.
Sophie was born in Carnpore, India in about 1820 and it is very likely that her father was a lieutenant Thomas Jenour of 14th Buckinghamshire Regiment, 2nd battalion. Her marriage certificate shows that her father was indeed Thomas Jenour, although by the time of her marriage his occupation was scripture reader and not an army officer.
There is a pallots marriage record of Thomas Jenour's marriage to Mary Cole in Newport, Hampshire on January 19th 1813 and also a record of him passing through Malta in 1810 either travelling to or returning from India.
Assuming that the family account of an ancestor who was an officer in the British army, serving in India is correct, then from the information gleaned from the records, this is the most likely explanation.
As for being wealthy, Thomas Jenour was probably the son of Joshua Jenour a once wealthy London newspaper publisher who reputedly spent his vast fortune and left his family improverished and records from the Isle of Man show that Thomas himself became bankrupt there in the late 1820s. Thomas moved to Liverpool as a warehouseman before becoming a teacher/scripture reader and although I have found no record of him with his daughter Sophie she too must have been in the Liverpool area as she married Thomas Hallows in the West Derby district.
However, improverished is probably a relative term and to their neighbours in the north west of England in the late 19th century Sophie Hallows may have seemed to have more comfortable means than most. I don't know, but to me her address and employment circumstances do not suggest someone well off, but it's possible she had received a small inheritance from her grandmother Harriet (abandoned wife of Joshua Jenour) the daughter of Mr and Mrs Andrews, wealthy land owners and the subjects of the painting by Constable.