public UniqueValueRendererDefinition()

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);
    });

}