Change line color once it reaches above/below a value

Hi guys, how do I change the color of the Aroon line once it reaches above 50 and below -50?  I want to create an indicator like the picture shown below.

Please note that I'm not a coder and have no experience in programming language but here's the code I've done so far. Any advice will be much appreciated, thanks!

namespace cAlgo.Indicators
{
    [Levels(100, -100)]
    [Indicator(AccessRights = AccessRights.None)]
    public class AroonCombined : Indicator
    {
        private Aroon _aroon;

        [Parameter(DefaultValue = 25)]
        public int Period { get; set; }

        [Output("Combined", PlotType = PlotType.Line)]
        public IndicatorDataSeries Combined { get; set; }



        protected override void Initialize()
        {
            _aroon = Indicators.Aroon(Period);
        }


        public override void Calculate(int index)
        {
            double val = (_aroon.Up[index] + -_aroon.Down[index]);
            Combined[index] = val;

        }

    }


}