public UniqueValueRendererDefinition( 
   List<string> fields,
   CIMSymbolReference symbolTemplate,
   CIMColorRamp colorRamp,
   CIMSymbolReference defaultSymbol,
   bool useDefaultSymbol
)

public async Task ApplyColorRampAsync(FeatureLayer featureLayer, List<string> fields)
{

    StyleProjectItem style =
        Project.Current.GetItems<StyleProjectItem>()
            .FirstOrDefault(s => s.Name == "ColorBrewer Schemes (RGB)");
    if (style == null) return;
    var colorRampList = await QueuedTask.Run(() => 
                style.SearchColorRamps("Red-Gray (10 Classes)"));
    if (colorRampList == null || colorRampList.Count == 0) return;
    CIMColorRamp cimColorRamp = null;
    CIMRenderer renderer = null;
    await QueuedTask.Run(() =>
    {
        cimColorRamp = colorRampList[0].ColorRamp;
        var rendererDef = new UniqueValueRendererDefinition(fields, null, cimColorRamp);
        renderer = featureLayer?.CreateRenderer(rendererDef);
        featureLayer?.SetRenderer(renderer);
    });

}

await QueuedTask.Run(() =>
{
  var fields = new List<string> { "Type" }; //field to be used to retrieve unique values
  CIMPointSymbol pointSym = SymbolFactory.Instance.ConstructPointSymbol(
      ColorFactory.Instance.GreenRGB, 16.0, SimpleMarkerStyle.Pushpin);  //constructing a point symbol as a template symbol
  CIMSymbolReference symbolPointTemplate = pointSym.MakeSymbolReference();

  //constructing renderer definition for unique value renderer
  UniqueValueRendererDefinition uniqueValueRendererDef =
new UniqueValueRendererDefinition(fields, symbolPointTemplate);

  //creating a unique value renderer
  var flyr = MapView.Active.GetSelectedLayers()[0] as FeatureLayer;
  CIMUniqueValueRenderer uniqueValueRenderer = flyr.CreateRenderer(uniqueValueRendererDef) as CIMUniqueValueRenderer;

  //setting the renderer to the feature layer
  flyr.SetRenderer(uniqueValueRenderer);
});