King's Colour

"The flag of Great Britain, often referred to as the King's Colour, Union Flag, Union Jack, and British flag (retroactively prefixed as being the 'first' such flag, in order to distinguish it from the modern flag of the United Kingdom), was used at sea from 1606 then more generally from 1707 until 1801 as the flag of the Kingdom of Great Britain, and is the precursor to the modern Union Jack." -- Wikipedia