The Visual options dialog is designed to change notebook visual appearance in tree and to change the notebook images. The dialog consists of three pages: Visuals, Images and Margins.

On Visuals page you can change the appearance of notebook in tree: choose the image, color and font style for notebook. Check the Example pane when changing visuals.

On Images page you can customize the notebook's images set. The toolbar allows to do the following:

Add image(s) - add the images from .BMP files. These BMPs should have 16x16 size. Otherwize they will be separated to 16x16 pieces.
Delete selected image(s) - remove selected image or several images from notebook
Replace selected image - replace selected image with new image from .BMP file.
Save images to one file - save notebook images to BMP "imagelist". Useful to distribute your own image list and add it to other notebook with several clicks.
Save selected images to separate files - just save selected images to several files. You'll be asked for a base file name. All images will get a name like Image-01.bmp, Image-02.bmp (if you've entered 'Image').
Restore the original image list - cancel all changes you've made in this dialog with image list and restores the original one.
Set as default image for current notebook - sets selected image as a default image for all newly created notes in current notebook.

On Margins pane you can change the default page margins for newly created notes in current notebook. Press 'Change default margins...' button to do it.