By default it saves to a /bakes/ folder next to your .blend file (the path //bakes/ is relative to the blend). You can change the Output Path in the panel to any absolute or relative directory before baking. The file is named BakeDiffuse_.png.

Settings are saved to uv_shell_colorizer_settings.json next to your .blend file — not globally. If your .blend file has not been saved yet, or if the JSON file has been deleted, the addon will fall back to defaults. Save your .blend file first, then configure the addon settings and they will persist on next open.

Yes, that is one of the core features. Select as many mesh objects as you want in the 3D Viewport and click Colorize UV Shells once — all selected meshes are processed in a single pass. Each object's islands are colorized independently so there is no color overlap between objects.

Only if you forget to clean up. The addon creates temporary viewport materials for visualization. Click Remove Shell Materials before your final render to restore the original state. The cleanup is non-destructive — it only removes materials prefixed with UVShell_ and never touches anything else on the object.