i solved the problem in this way:
in the first part of the code it is defined my textfield style...
self.hRepositoryTextfield.SetStyle(0, len(self.hRepositoryTextfield.GetValue()), wx.TextAttr(wx.RED))
self.hRepositoryTextfield.SetFont(self.hFontLabel)
self.hRepositoryTextfield.Bind(wx.EVT_TEXT, self.forceDefaultStyle)
... then i bind every text change to my forcing-style function:
def forceDefaultStyle(self, event):
hEventObject = event.GetEventObject()
hEventObject.SetStyle(0, len(self.hRepositoryTextfield.GetValue()), wx.TextAttr(wx.RED))
hEventObject.SetFont(self.hFontLabel)
and it works!