The ideal corn is small hard yellow grain, such as popcorn. Avoid soft wheat, hard winter wheat is excellent. Do not store large quantities of grain during warm weather. Keep grain dray at all times. While greens are not required, they are a welcome addition to the pigeon's diet.
Green food can be practically any fresh green leafy vegetable.
When feeding grain, you also need to provide grit for the birds. Again mixtures can be purchased from the same stores you buy grain from. The birds get minerals from the grit. They also need the grit so that they can grind the grains in the gizzard to be easily digested. Water is extremely important for pigeons.