Paul

You are welcome. It appears that the grey facings were worn by non-regular units. (e.g. The New Romney Fencible Cavalry (Duke of York's Own) had Kentish grey facings....)

A quick look in various Regimental Histories of Militia Regiments seems to indicate that regulation uniforms were worn with regimental distinctions, if any. You can find a number of histories on google books searching on Historical Records of British Militia. I imagine there was less latitude in selection of uniforms for the Militia than used by the Volunteers.

Good hunting.

Ron