The image shows an 18 inch Madame Alexander doll (similar in body style to the American Girl dolls) wearing a sleeveless shirt and matching skirt. They’re made of a confetti-print fabric in many colors on a white background.
Click on the link in the caption, and it will take you to a page where you can download and print all the free printable sewing patterns for making these doll clothes, along with links to tutorial videos that show you how to make this outfit.