I have a dark theme and I selected a gray colour for the horizontal line in the menu of the Pencil button, but when I set an alert on this line, it turns black and merges with the dark chart, where can I change the colour of the alert separately?

The MoonBot terminal does not explicitly set the alert colour because this colour is inverted relative to the base colour of the drawing element without alert. For example, if you assign a gray base colour to the drawing element and then set alert on it, the colour of the drawing element will become black and it will blend in with the background of the graphic in the dark design theme. In this case, select such a base colour, the inversion of which will also be clearly visible on the background of the graphic. For example, you can set the base colour for a horizontal line to green, then the colour of this line will be yellow and both colours will be well visible against the dark background of the chart.