Kelsey plums are very large green heart-shaped plums that are yellow inside when they're first picked. Although Kelsey plums are sweet and ready to eat even when firm and green on the outside, as they get softer the skin and inside becomes yellow to pink. You can eat them in all their different stages of color and texture. Kelsey is an old variety of Japanese plum similar to European Green Gage plums.
In the photo above you can see a box of just-picked Kelseys with a natural wax bloom that makes them look blueish. In the photo below, a Kelsey is cut open so you can see the inside. We now have Kelseys for sale in the fruit stand in various stages, from green to yellow-red.