title: JTextField: Change the foreground color and save the content
body: <p>I have a frame with some <code>JTextFields</code> for the user insert some values.
  When the window is opened, the text fields have written, in gray, what the user should write in that container, like "value in seconds"...</p>
  
  <p>I want to change the color of those letters (I think it is the foreground) to dark when the user starts to write in the <code>JTextFields</code>, and save to a <code>String</code> what is written by the user.</p>