Red Square Castle is a building with a long history and unique cultural connotation. It not only represents the traditional Russian culture, but also witnessed the historical development of Russia. Therefore, when creating paintings about Red Square Castle, we can make creative explanations from the following aspects:

1. Highlight architectural features: Red Square Castle is a building full of baroque style, with a unique and gorgeous appearance, which can highlight its characteristics in painting, such as the spire of the castle, complex decoration, fine carving and so on.

2. Expression of historical background: Red Square Castle is the witness of Russian history, and its historical background can be expressed by painting, such as depicting some historical events and people around the castle, so that viewers can feel the historical and cultural details of the castle.

3. Color: The appearance of the Red Castle is mainly red, and bright colors, such as red and gold, can be used in painting to highlight its gorgeous and mysterious characteristics.

4. Use light and shadow: Light and shadow can be used in painting to express the three-dimensional sense and layering of the red castle, such as depicting the details and texture of the castle through the angle and intensity of light irradiation.

5. Incorporate modern elements: On the basis of maintaining tradition, modern elements can be incorporated into paintings, such as using some modern painting techniques and styles to make the works more modern.

To sum up, when creating paintings about Red Square Castle, we can creatively explain them from the aspects of architectural characteristics, historical background, color application, light and shadow expression, modern elements and so on, so as to make the works more cultural and historical.