Studies have been done that show your mind can even assign a difference of flavor to an object just because of a difference in texture, or especially, color.
Either way it goes - it could be your bird likes the shape or color over the other ones, or it could be a preference of flavor. I found my Sun Conure, Chicken, always was more willing to try very brightly colored foods in the yellows and orange hues.
He was hard-pressed to try anything dark, though eventually came to love blueberries and red raspberries.