SHADE BORDER                                                       <Alt>+I

  When you have drawn a border using line characters, you can use this
  function to give the border a shaded or "pressed metal" effect. It does
  this by setting the the top and left edges of the border to white, the
  bottom and right edges to dark gray, and the top right and bottom left
  corners to light gray.

  However, if you don't like those colours you can specify your own by
  pressing <Alt>+I when the cursor is over a character that isn't a line
  character. An attribute box will then pop up so you can specify the
  colours you want. The first colour is the "top left" colour, the second
  is the "bottom right" colour, and the last is the "corner" colour.

  Note that in these selections only the text colour is relevant - the
  background colour is left as it is. However, if you set the "corner"
  colour to black on black, it won't have any effect - only the "top left"
  and "bottom right" colours will be used.