congratulations on your new Oscar. Juvenile Oscars will change color as they get older. At the moment, I would feed your Oscar three times a day. There are loads of things you could feed him, small pellets, Krill, shrimp, bloodworm. Remember that even though 2 1/2 inches isn't that big, they still have big mouths and can probably eat bigger food than other fish of the same size. Just be careful though, baby Oscars are absolute pigs and will cram as much as they can get into their mouths, so don't put too much food in at once.