FlatButton Selected-Property not workt

Hi, thx for your answer.
How to get, that at the start of application one of buttons is selected?

That does not work.
Button have then selected state! Yes. But it does not change its color to ActiveColor.

I have two diffrtrent colors for Active(RED) and Normal(BLACK).
Two buttons, both have isTab=true

App start:
public Form1()
{
InitializeComponent();
bunifuFlatButton1.selected = true;
}

bunifuFlatButton1 color is BLACK!