backface culling not marking faces as red and blue

Question

I remember backface culling used to mark flipped normals as red and correct ones as blue. Not sure if it's different with the newer versions, but backface culling is now only displaying the flipped normals as invisible for some reason

How do I set this to mark the faces as red and blue like it used to?

Answer 1

Backface culling is a feature that hides backfaces. It is not supposed to mark them in any way, but prevent them from being rendered. If you wish to show backfaces, you need to enable Face Orientation overlay in the Overlays menu in the 3D Viewport:

Note that you need Backface Culling to be off for the material so that the backfaces are visible and the overlay is shown on them. If it's on, you will not be able to see the overlay as well for the backfaces, because they will not be rendered(in the viewport) at all.

It's also possible to choose the colors of the overlay in the Preferences, Themes tab, under 3d Viewport color section and it might be convenient to set the alpha of positive direction to 0 to not show it at all so you can still see your materials on the "good" side in Material Preview shading mode while working with this overlay on.

Answer 2

In addition to Martynas Žiemys' answer, I want to point out that you can make Blender colour the backfaces differently while still colouring the front faces normally. This is done by making the front face colour transparent.

So the full process then goes like this:

• Open the overlays menu in the top right, click Face Orientation.
• Edit -> Preferences -> Themes 3D Viewport.
• Less than half-way down the list, find Face Orientation Front and set its alpha to 0.
• If you want this applied to all projects, click the menu button bottom left and click Save Preferences.