public class UnclassedColorsRendererDefinition : RendererDefinition 

{
    string colorBrewerSchemesName = "ArcGIS Colors";
    //Get the style project item that contains the color ramps
    //Refer to the Initialize region for an example of how to get a style item
    //Note: Run within a QueuedTask
    CIMPointSymbol pointSym = SymbolFactory.Instance.ConstructPointSymbol(ColorFactory.Instance.GreenRGB, 16.0, SimpleMarkerStyle.Diamond);
    CIMSymbolReference symbolPointTemplate = pointSym.MakeSymbolReference();

    //defining an unclassed renderer with custom upper and lower stops
    //all features with value >= 5,000,000 will be drawn with the upper color from the color ramp
    //all features with value <= 50,000 will be drawn with the lower color from the color ramp
    UnclassedColorsRendererDefinition unclassRndrDef = new UnclassedColorsRendererDefinition
                          ("Population", symbolPointTemplate, colorRamp, "Highest", "Lowest", 5000000, 50000)
    {

        //drawing features with null values with a different symbol
        ShowNullValues = true,
        NullValueLabel = "Unknown"
    };
    // Create a point symbol for null values
    CIMPointSymbol nullSym = SymbolFactory.Instance.ConstructPointSymbol(ColorFactory.Instance.RedRGB, 16.0, SimpleMarkerStyle.Circle);
    unclassRndrDef.NullValueSymbol = nullSym.MakeSymbolReference();
    //Create the unclassed renderer using the definition
    CIMClassBreaksRenderer cbRndr = featureLayer.CreateRenderer(unclassRndrDef) as CIMClassBreaksRenderer;
    //Set the renderer to the feature layer
    featureLayer.SetRenderer(cbRndr);
}

/// <summary>
/// Renders a feature layer using an unclassed color gradient.
/// ![cb-unclassed.png](https://ArcGIS.github.io/arcgis-pro-sdk/images/Renderers/cb-unclassed.png "Class breaks unclassed renderer.")
/// </summary>
{
  //Check feature layer name
  //Code works with the USDemographics feature layer available with the ArcGIS Pro SDK Sample data
  var featureLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>().FirstOrDefault(f => f.Name == "U.S. National Transportation Atlas Interstate Highways");
  if (featureLayer == null)
  {
    MessageBox.Show("This renderer works with the U.S. National Transportation Atlas Interstate Highways feature layer available with the ArcGIS Pro SDK Sample data", "Data missing");
  }
  //Gets the first numeric field of the feature layer
  var firstNumericFieldOfFeatureLayer = "NumericFieldInFeatureLayer";
  //Gets the min and max value of the field
  //Refer to the GetFieldMinMax function below
  var labels = GetFieldMinMax(featureLayer, firstNumericFieldOfFeatureLayer);
  UnclassedColorsRendererDefinition ucDef = new UnclassedColorsRendererDefinition()
  {
    Field = firstNumericFieldOfFeatureLayer,
    ColorRamp = colorRamp,
    LowerColorStop = Convert.ToDouble(labels.Item1),
    UpperColorStop = Convert.ToDouble(labels.Item2),
    UpperLabel = labels.Item2,
    LowerLabel = labels.Item1,
  };
  //Note: Run within QueuedTask
  CIMClassBreaksRenderer renderer = (CIMClassBreaksRenderer)featureLayer.CreateRenderer(ucDef);
  featureLayer?.SetRenderer(renderer);
}