You could use the button_Down and button_Up events.
B4X:
Sub button1_Down
Dim cd As ColorDrawable
cd.Initialize(Colors.ARGB(100,50,50,250),0dip)
button2.Background = cd
End Sub
Sub button1_Up
Dim cd As ColorDrawable
cd.Initialize(Colors.ARGB(255,50,50,250),0dip)
button2.Background = cd
End Sub