To preview a 3D texture, do one of the following:
To preview a 3D texture, select the texture in the Project window. In the Inspector window, Unity displays the preview of the texture at the bottom of the Texture Import Settings window.
There are three different 3D texture preview modes available:
Refer to 3D texture preview reference for more information.
Use the Handles API to draw the 3D texture in the Scene view. The Handles API lets you use custom gradients and configure how you draw the texture.
Refer to the following for more information: