Ah! I have noticed that this year in New York, the plants haven't grown that well. My dad started some plants from seeds, they all died (mind you, when we put them in the ground, they were healthy but a day later they were dead). We also grew some store-bought eggplants. Nothing but the leaves came up. It's not a good year for growing things. Your eggplants are yellow most likely because the soil isn't healthy this year thanks to global warming and environmental problems.