Background
You can set the background color of the story canvas through a special control with type background:
.ladle/components.tsx
export const argTypes = {
  background: {
    control: { type: "background" },
    options: ["purple", "blue", "white", "pink"],
    defaultValue: "purple",
  },
};
This will make it accessible to all stories through the standard control's UI. You can also set it per story level as other controls and even override the global settings:
src/hello.stories.tsx
export const Story = () => <div>Hello</div>;
Story.argTypes = {
  background: {
    name: "Canvas background",
    control: { type: "background" },
    options: ["green", "yellow", "pink"],
    defaultValue: "pink",
  },
};
Note that there can be only one active background control.