As long as he is pooping and there is color in the poop, then he is eating. The only concern would be very bright green droppings as this can be a sign of starvation. I always recommend feeding what he was eating at the store, which was most likely seeds, and then after a couple of weeks, start working on converting him to a healthier diet like pellets or our foraging diets.
If he is eating seeds now, you can blow on the dish of seeds and if he ate, a bunch of hulls will blow away, because he will remove these and most birds drop the empty hulls back into the bowl. However, they do not always know to dig under the hulls for good seed, so they can actually starve to death with a half dish of seeds, that are covered in empty hulls. This is why it is important to feed him daily and check his cup in the afternoon. You can blow the hulls off or shake the cup to bring the whole seeds to the top. I’ll give you the link to our feeding guide to give you some ideas on healthy foods and how to convert him to a better diet than loose seeds.
Bird Food Guide
Thank you for Asking Lafeber,