I think you’ve selected surfaces versus bodies when choosing the colors. You want to double tap to ensure you get the body. To go back, you’ll want to have all the bodies selected, and the choose a mundane color (light gray perhaps).
You can also use the component viewer to select the bodies.
Press cmd + a, use area selection, or the Items panel to select everything in the workspace, then press Change material in the materials sidebar, and select the default material. This way everything is set back to the default.
Tried this a few times - selecting everything from the items list and then to properties on the visualization screen. Dragged out the default color and everything changed. When leaving visualization though nothing has changed on the modeling screen.
Fwiw - this is the free version. When I leave the visualization screen I have to choose to remove all materials or subscribe. Maybe I have found a bug?
For example, if you import a file where colors and materials are changed, they will remain, since “editing” materials is the paywalled feature. You can also use the full feature set during the free trial.