public UniqueValueRendererDefinition()

{
    List<string> fields = new List<string>() { "Field1" };
    //Note: Needs QueuedTask to run
    StyleProjectItem styleToUse =
      Project.Current.GetItems<StyleProjectItem>()
          .FirstOrDefault(s => s.Name == "ColorBrewer Schemes (RGB)");
    if (style == null) return;
    //Note: Needs QueuedTask to run
    var colorRampListFound = styleToUse.SearchColorRamps("Red-Gray (10 Classes)");
    if (colorRampListFound == null || colorRampListFound.Count == 0) return;
    CIMColorRamp cimColorRamp = null;
    CIMRenderer renderer = null;

    cimColorRamp = colorRampListFound[0].ColorRamp;
    var rendererDef = new UniqueValueRendererDefinition(fields, null, cimColorRamp);
    renderer = featureLayer?.CreateRenderer(rendererDef);
    featureLayer?.SetRenderer(renderer);
}

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

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

    //creating a unique value renderer
    CIMUniqueValueRenderer uniqueValueRenderer = featureLayer.CreateRenderer(uniqueValueRendererDef) as CIMUniqueValueRenderer;

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