The sides of the bilayer (see diagram) are the same for all internal membranes but flipped/opposite colors for the plasma membrane.
Work Step by Step
The lipids on one side of the bilayer are designed to face/withstand chemical conditions on that side as well as to provide function on that side. The flipping of the bilayer sides from the endomembrane system to the plasma membrane thus makes sense. You can see it in the diagram in that the same color layer always faces the cytoplasm.