Hello,

Typically plants with aster yellows will be chlorotic, stunted, and generally not very healthy looking. I do not think this looks like an aster yellows symptom. When a plant has aster yellows, the flowers are more distorted and the petals do not color as they should. You can look at some example photos comparing aster yellows to other coneflower pests here: https://bygl.osu.edu/node/1634

Your flower looks like one of the disc florets simply exhibited as a ray floret, not something to be concerned about :)