ComposedLookDefinitionMasterPageUrl Field

Specifies the URL of the master page file. If the composed look should be displayed in the 'Change the look' page, the masterpage must be located in the current site and a corresponding .preview file must exist, otherwise a masterpage from the current site collection can be used. E.g.: '{Web.ServerRelativeUrl}/_catalogs/masterpage/myMaster.spcolor'

public PatternString MasterPageUrl