Transparency, added to AutoCAD® (and AutoCAD® Architecture) in the 2011 release, is now fully integrated into AEC objects and the AutoCAD Architecture Display System. Previously, Transparency could be applied to the main object only, by using the tools on the Transparency panel on the Home ribbon tab. Entity Transparency is now an editable property for parent AEC objects, on the Design tab of the Properties palette, in the Basic category, General subcategory.
Transparency as a Display Property in Style Manager - Display Theme
Transparency as a Display Property in Style Manager - Layer Key Style
Transparency as a Display Property on the Display Tab of the Properties Palette - Wall Object
Transparency as a Display Property via the Object Display Dialog - Wall Object
Transparency as a Display Property of a Material Definition
Keep in mind that Transparency works like any other object property: the value applied to a nested object will take precedence over that of the parent obejct. In 2011 and 2012, the only option was to apply Transparency to the parent object (for example, a Wall). Setting an explicit Transparency value to a Wall object would make the Wall display with the Transparency set. Doing the same in ACA 2013 will only make the Wall transparent at that value if the display of all of the Wall's components is set to be "ByBlock" (or just happens to be hard coded to that same value). For components whose display is controlled by an assigned Material Definition, then the Transparency of the active component of the Material Definition would need to be set to "ByBlock". When opening files created in previous versions, it appears as though the component values default to ByBlock, which would preserve the previous behavior.
Next Article in the Series (ACA 2013: Object Display Enhancements Part 3)