Reinier,

> when using Squeak under AIX via Exceed (a Windows95 X terminal client) the
> blue button is available by using Ctrl+Left mouse button (red button)
> Does anyone know if this is the normal behavior under Unix?

Perfectly normal.  Here's the relevant snippet of sqXWindow.c:

  switch (theEvent->button)
    {
    case 1: stButtons= 4; break;
    case 2: stButtons= 2; break;
    case 3: stButtons= 1; break;
    default: ioBeep(); break;
    }

  if (stButtons == 4)	/* red button honours the modifiers */
    {
      if (theEvent->state & MOD_CONTROL)
	stButtons= 2;	/* yellow button if CTRL down */
      else if (theEvent->state & MOD_META)
	stButtons= 1;	/* blue button if META down */
    }

(theEvent is an XButtonEvent, and X numbers the buttons from
left-to-right starting at 1.  Squeak has a separate bit for each
button, with the rightmost button in the least significant bit.)

Regards,

Ian