There is a ProGuide for styling: ProGuide Style Guide · Esri/arcgis-pro-sdk Wiki · GitHub and there are references for brushes and colors:
And here is some sample code that might be of help: arcgis-pro-sdk-community-samples/Framework/Styling-with-ArcGIS-Pro at master · Esri/arcgis-pro-sdk-c...
I have read and review all of this but still the only way to use Esri styles and brushes is through DynamicResources. I can't find nothing in SDK where I would be able to do this but with Esri Brushes
TextBlock descrip = new TextBlock()
Visibility = Windows.Visibility.Visible,
TextWrapping = TextWrapping.Wrap,
TextTrimming = TextTrimming.CharacterEllipsis,
Background = Media.Brushes.Black
You can try something like this code snippet below. All the Esri brushes are listed in the wiki page shared by Wolf above.
var esriBrush = Application.Current.Resources["Esri_BorderPressedBrush"] as Brush; textBlock.Foreground = esriBrush;