The standard material has been replaced!

I am having a problem that never happened in all the years since I started using Sketchup. It may be a dumb question but since it never happened to me I do not know how to solve it.

When one starts modeling something there is no material attached to the shape created; in general it is white on one side and, say, gray on the backside. In one specific file when I create a rectangle it comes out with a material, in this case a pebble material, without my intending it to be so.

Any ideas as to how to get back to the original status? Thanks in advance.

Check the active style and see if the front and/or back side materials for the default have been edited. Technically the “default material” is the absence of a material, and the SketchUp renderer uses those items from the style in that situation.