1st off, thanks to ThinkDecoded for converting my TOS code over to NinjaTrader 8. It works properly when I hard code the colors for up/down conditions.
Example:

// Cambiar colores según la tendencia
PlotBrushes[0][0] = emaSeries[0] > emaSeries[1] ? System.Windows.Media.Brushes.White : System.Windows.Media.Brushes.Black;
PlotBrushes[1][0] = smoothingLine1[0] > smoothingLine1[1] ? System.Windows.Media.Brushes.LightGreen : System.Windows.Media.Brushes.Red;
PlotBrushes[2][0] = smoothingLine2[0] > smoothingLine2[1] ? System.Windows.Media.Brushes.LightGreen : System.Windows.Media.Brushes.Red;
PlotBrushes[3][0] = smoothingLine3[0] > smoothingLine3[1] ? System.Windows.Media.Brushes.Blue : System.Windows.Media.Brushes.Purple;


However the color selection inside the setting dialog for each EMA does not work. I tried to message ThinkDecoded about it, but haven't received an answer.
Here is the code. Any help would be greatly appreciated, Thanks!

Code:
#region Using declarations
using System;
using NinjaTrader.Gui.Tools;
using NinjaTrader.NinjaScript;
using NinjaTrader.Data;
using NinjaTrader.Gui.Chart;
using System.Windows.Media; // Necesario para Brushes
#endregion

namespace NinjaTrader.NinjaScript.Indicators
{
public class MultiSmoothedEMA : Indicator
{
private EMA emaSeries;
private EMA smoothingLine1;
private EMA smoothingLine2;
private EMA smoothingLine3;

[NinjaScriptProperty]
public int Length { get; set; } = 50;

[NinjaScriptProperty]
public int SmoothingLength1 { get; set; } = 5;

[NinjaScriptProperty]
public int SmoothingLength2 { get; set; } = 10;

[NinjaScriptProperty]
public int SmoothingLength3 { get; set; } = 15;

protected override void OnStateChange()
{
if (State == State.SetDefaults)
{
Description = "Indicator with EMA and multiple smoothed lines.";
Name = "MultiSmoothedEMA";
IsOverlay = true;

AddPlot(System.Windows.Media.Brushes.LawnGreen, "EMA Line");
AddPlot(System.Windows.Media.Brushes.Blue, "Smoothing Line 1");
AddPlot(System.Windows.Media.Brushes.Blue, "Smoothing Line 2");
AddPlot(System.Windows.Media.Brushes.Black, "Smoothing Line 3");
}
else if (State == State.DataLoaded)
{
emaSeries = EMA(Close, Length);
smoothingLine1 = EMA(emaSeries, SmoothingLength1);
smoothingLine2 = EMA(emaSeries, SmoothingLength2);
smoothingLine3 = EMA(emaSeries, SmoothingLength3);
}
}

protected override void OnBarUpdate()
{
if (CurrentBar < Math.Max(Length, Math.Max(SmoothingLength1, Math.Max(SmoothingLength2, SmoothingLength3))))
return;

// Asignar valores a los plots
Values[0][0] = emaSeries[0];
Values[1][0] = smoothingLine1[0];
Values[2][0] = smoothingLine2[0];
Values[3][0] = smoothingLine3[0];

// Cambiar colores según la tendencia
PlotBrushes[0][0] = emaSeries[0] > emaSeries[1] ? System.Windows.Media.Brushes.White : System.Windows.Media.Brushes.Black;
PlotBrushes[1][0] = smoothingLine1[0] > smoothingLine1[1] ? System.Windows.Media.Brushes.LightGreen : System.Windows.Media.Brushes.Red;
PlotBrushes[2][0] = smoothingLine2[0] > smoothingLine2[1] ? System.Windows.Media.Brushes.LightGreen : System.Windows.Media.Brushes.Red;
PlotBrushes[3][0] = smoothingLine3[0] > smoothingLine3[1] ? System.Windows.Media.Brushes.Blue : System.Windows.Media.Brushes.Purple;
}
}
}

Joseph H 

\ However the color selection inside the setting dialog for each EMA does not work. I tried to message ThinkDecoded about it, but haven't received an answer. Here is the code. Any help would be greatly appreciated, Thanks!

You need to Serialize the Brushes.. link and example attached.

https://ninjatrader.com/support/helpguides/nt8/NT%20HelpGuide%20English.html?user_definable_color_inputs.htm