TPopupNotifier was not designed to be particularly customisable.
The Text content is painted via a private TLabel, which is not accessible except through heavy hacks, so the font colour is to all intents and purposes fixed as clBlack.
The size of the window is hard-coded as 325 x 110. However, the THintWindow used for display is a public property, so if you really want to you can do limited size adjustments of this sort:
procedure TForm1.ButtonShowPopupClick(Sender: TObject);
const
aText ='This is a longish string to test how well TPopupNotifierEx performs when given'+
' a fairly long string to work with. Note this is just a test.';
var
r: TRect;
begin
PopupNotifier1.Title:='Resize test';
PopupNotifier1.Text:=aText;
r:=PopupNotifier1.vNotifierForm.CalcHintRect(110, aText, nil);
PopupNotifier1.vNotifierForm.HintRect:=r;
PopupNotifier1.vNotifierForm.Width:=r.Right-r.Left + 50;
PopupNotifier1.vNotifierForm.Height:=r.Bottom-r.Top + 10;
PopupNotifier1.Visible:=True;
end;