When creating a sales document, a green or red symbol is displayed in the line, depending on whether the product is available in the warehouse or not. This is very practical at first, but unfortunately "red" does not mean that nothing is available (but draft SO's could exist) - just as "green" does not mean that the product is available. (I haven't quite understood the logic behind "green" yet - could it be that PO's are also taken into account?) Why is this so complicated? Couldn't one simply make "freely available = green" and "not freely available = red", i.e. take into account the stock minus reservations? 
Or have I just not understood it yet?