Appearance defines how color, material and texture images are applied as the visual characteristics of a shape.
Appearance is individually associated with specific geometry within a shared Shape node. Each Appearance is a container node that can include Material, TwoSidedMaterial, ImageTexture, MovieTexture, PixelTexture and MultiTexture nodes.
Appearance can also contain property nodes for controlling rendering and texture: FillProperties, LineProperties, TextureProperties, TextureTransform and MultiTextureTransform nodes.
The supporting Chapter 5 slideset and course videos (NPS, YouTube) for X3D for Web Authors are available online via X3dGraphics.com.
Also available: X3D Scene Authoring Hints for Images and Videos and URL Links.
This viewpoint slideshow is online at https://X3dGraphics.com/examples/X3dForWebAuthors/Chapter05AppearanceMaterialTextures/viewpointSlideshow.html
Viewpoint image version history at https://sourceforge.net/p/x3d/code/HEAD/tree/www.web3d.org/x3d/content/examples/X3dForWebAuthors/Chapter05AppearanceMaterialTextures/_viewpoints