The colours of the cube that is displayed is dependent in the colour table that you have attached to the file so if you have the autocad.tbl attach the cube colours are yellow on inside the SWA and green on element outside SWA.

I believe that in the positions of the colours in the colour table is how the colours are chosen, the first color position is 0 which is White. So, the red color comes at the 3rd position and green color comes at the 2nd position. But for your file, at 3rd position there is Green and at 2nd position there is Yellow. That is why, when no element is placed outside the SWA, the SWA color remains Yellow (instead of Green) and when any elements are placed outside the SWA, the SWA color changes to Green (instead of Red).