Where as the Royal Army has set regulations for it's Colours, the Militia has taken a very liberal approach to the procurement if it's flags.
Basically the design of the flags are approved by the Regimental CO, with final approval to come from the King. This is rarely done however, with the King often seeing a particular Militia Regiment's flag for the first time when either conducting an inspection or on the field of battle!
Militia Regiments carry only one flag, a "Regimental" or "Colonel's" Colour.
Flags are often designed by an individual from the regiment, (and sometimes the wife of the CO, RSM, 2IC etc). Occasionally they are a collective effort, such as the Clairmont Militia's Regimental Colour. Their colour was selected by vote after the CO ran a compitition. The Best design (as voted on by the Officers and RSM) would earn the budding "Artist" an extra seven rations of Rum!
Consequently some of the most bizarre and / or impressive flags belong to the Militia Regiments.
Example of some are below: