ddo you have the seedlingsin soil, what size pots, need pics, you dont need to water them unless the soil feels dry 1 or 2 inches deep in the pot. the purple color means your room temps are falling below 69 or so so you might need more heat, but purple isnt a problem cause you can grow below 69, it sounds like your over watering, good lighting is the most important, just only water enough to fill the container its in and then you water again when theres almost no water left.