If your scene contains more high resolution textures than your video card has enough memory to handle, an error message appears, textures do not load, and your scene appears in non-textured mode.
To mitigate this, select
Renderer > Viewport 2.0 >
from the panel menus, and enable
Clamp Texture Resolution.
When this option is enabled, any textures with a resolution above the
Max Texture Resolution value are downscaled so that you can still work in textured mode while saving memory. See
Troubleshoot "GPU texture ram exceeded, texture loading failed" error message and
Viewport 2.0 options.
In addition, you can select among different texture loading modes in the Display section of the Preferences window. Select Immediate mode for the fastest scene loading time; however, you may have to wait briefly before you can interact with your scene. Alternatively, you can select Parallel mode so that you can interact with your scene while materials realize and textures load. See Display preferences.