It could be that the plants were damaged during transplanting. Or they could be turning yellow because they were given too little or too much water after transplanting. Either practice can damage the root system and lead to yellowing foliage. They also could be suffering from being planted too deeply-especially in clay soil. Lack of oxygen resulting from deep planting damages the roots. Have you fertilized them? Accidentally giving them too much fertilizer-especially right after transplanting them-could also have caused yellowing and browning of the foliage. Also, hostas often turn yellow by the end of the season. It could be that they'll come back just fine next year.