innerColor

Specifies the color of the point mark when hovered with the mouse:

seriesSettings: {
    polarsplinearea: {
        pointMark: {
            enabled: true,
            activeSettings: {
                pointHoveredState: {
                    enabled: true,
                    innerColor: "red"
                }
            }
        }
    }
}

This setting is demonstrated in the following example.