White surrounding flange for the built in domestic ducted vacuum system flap valves, see   These are the Vaculine brand from Canada.

Mounted Horizontal or Vertically, they neaten up the fitting between the outlet and the wall, especially if the plaster is crumbling or the paint is chipping.

They make the outlet more attractive generally.

Choose either the usual WHITE however there is Almond and Black available, so select your variant.