ShapeContainerMixin.createFill

createFill(opts: PaintOptions): Paint;

// Create a solid red paint
layer.createFill({
  type: "SOLID",
  color: { r: 255, g: 0, b: 0 },
});

// Create a gradient with default positioning (spans shape width)
layer.createFill({
  type: "GRADIENT_LINEAR",
  stops: [
    { color: { r: 255, g: 0, b: 0 }, offset: 0, opacity: 1 },
    { color: { r: 0, g: 0, b: 255 }, offset: 1, opacity: 1 },
  ],
});