I've modeled a bigger scene and up until now I could see the image textures in material view. Now I changed one of the 3D-objects in edit mode, did not like it and pressed CTRL-Z several times to get back in history - but all of a sudden every material using an image texture shows up solid black in material view. The procedural materials are fine. I guess I missed the CTRL-Z and ended up with some unknown shortcut - but which one is ist? I already checked my textures - the uv-maps are all right, the maximum draw mode is okay, too, everything still renders fine.