In this diagram, we aim to visually represent a grid-based domain where robots paint tiles. Each element in the diagram has a specific visual representation to convey its status and identity:

1. **Shapes**:
   - **Rectangles**: Represent tiles on the grid. Each rectangle corresponds to a tile, and its position in the grid reflects the tile's location (e.g., top-left, directly below another tile).
   - **Circles**: Represent robots. Each circle is placed on the tile it currently occupies, indicating the robot's position.

2. **Colors**:
   - **Green**: Indicates a "clear" tile, meaning it is unoccupied and unpainted.
   - **Red**: Represents an "occupied" tile, where a robot is currently located.
   - **Gray**: Would represent a "painted" tile, indicating that the tile has been painted and is no longer clear. However, since the initial state does not have painted tiles, this color is used in the legend for future reference.
   - **White**: Represents a robot holding the white color. The robot circle is filled with white to indicate this status.
   - **Black**: Represents a robot holding the black color. The robot circle is filled with black to indicate this status.

3. **Sizes**:
   - **Tiles**: All tiles are of equal size, ensuring a uniform grid layout.
   - **Robots**: Slightly smaller than the tiles they occupy, allowing their placement on top of tiles without overlap.
   - **Color Availability**: Represented by smaller rectangles to the side of the grid, indicating that these colors are available for robots to switch to.

4. **Text Labels**:
   - Each tile and robot is labeled with its identifier (e.g., tile_0-1, robot1) to provide a clear reference to its position and status.
   - Text within each shape ensures that the label is associated with the correct object.

5. **Legend**:
   - Provides a mapping of colors to their meanings, ensuring that viewers can quickly understand the status of each tile and robot based on color alone.
   - The legend is positioned outside the grid to avoid overlap with the visual elements.

By using this combination of shapes, colors, and labels, the diagram effectively communicates the initial state of the domain, allowing viewers to understand the positions and statuses of tiles and robots at a glance.