If you look at the sun at dusk or dawn, you will see that it is not yellow but becomes red the closer it is to the horizon. Let's teach our object representing the sun to do the same by providing a property value source for it.
Open the QML document, find the declaration for the sunVisual object, and extend it with the highlighted part:
Rectangle { id: sunVisual // ... SequentialAnimation on color { ColorAnimation { from: "red" to: "yellow" duration: 0.2 * dayLength / 2 } PauseAnimation { duration: 2 * 0.8 * dayLength / 2 } ColorAnimation { to: "red" duration: 0.2 * dayLength / 2 } running: true }}