The various hats were used with different levels of dress, that is full formal dress, semi-formal dress, daily dress etc. If you were to look down at the bottom of the illustration, you would notice the variations of the regiments uniforms in khaki colour also.
A Colonel-in-Chief was the Patron of the Regiment. Which meant that the IF member who was the Colonel-in-Chief would attend the formal functions of the regiment, maybe even send collective presents to the regiment for Christmas and Easter. The IF member's patronage strenghtened the bond between the common soldier and the Imperial House.
The Imperial Guard Regiments were used for ceremonies, parades, etc. They were kept mainly in the Saint Petersburg area as a reserve military guard for the Imperial Family. Some of these guard units, as you probably already know, were stationed around Tsarsko Selo. They were not however, merely dress up toy soldiers, as there have been many occaissions in which these units have performed with great courage and
David
