Processing (like PDF and PostScript) uses a model where there is one global fill color (and stroke color) at all times.  That color applies to all subsequent drawing actions, until changed to something else.  So to make the rectangle a different color than the stuff that was drawn previous to it, you need to put a fill() call right before it.  Assuming you want the circles that's drawn after the rectangle to be the same as the circles that came before, you must then restore the fill to its previous setting.  So if you change these lines:

{
rect(160,0,140,90);
}

to this (by the way, you don't need the braces around the rectangle call for anything, so I got rid of them), you'll see what I mean:

// Make the rectangle red, just to make the change obvious:
fill(255,0,0,128);
// Draw it:
rect(160,0,140,90);
// Now restore the transparent green fill:
fill(178,255,0,190);