drawColor

Specifies the color of the point mark border when pointed to with the mouse:

seriesSettings: {
    stepline: {
        pointMark:
            {
                activeSettings:
                    {
                        pointHoveredState:
                            {
                                drawColor: 'red'
                            }
                    }
            }
    }
}

This setting is demonstrated in the following example.