Sorry, if this has been posted before.

At least, on on klm.se and klm.at the fare code is shown when you make a booking for an intercontinental flight. Click the "Show fare conditions" below the fare after selection of the flights.

If you want to see the conditions for intra-European flights, don't use the usual booking form but choose the multiple destinations option. Even though you just want to book normal return flights via Amsterdam (and not really multiple destinations), choose the flight from origin to destination and afterwards book the return flight. And voilą, you will see the "Show fare conditions" link which is invisible if you book the easiest way.

Still pretty bad compared with Finnair's and SN Brussels's booking engines, where you can choose how much you want to pay. You can see if a restricted business class fare is cheaper than flexible Y class fare. Finnair shows the exact booking class after choosing the flights and SN shows whether you get full or half miles.