Mark

In 1822 the order was:

Regulars/Marines
Fencibles/Militia
Yeomanry
Volunteers

Thus, Regulars/Marines had command of all others 'of equal degree belonging to other branches of the Military Service.'

So, no a Regular Ensign could not ignore a Militia Colonel. however, he was senior to a Militia Ensign regardless of date of commission.

Source: General Regulations and Orders for the Army: Adjutant General's Office 1822.

Good hunting.

Ron