your initial link is broken, but the second one worked.
When you sew one fabric on top of another in a decorative manner it's called applique. Doing stretchy applique on stretchy base is a good deal more challenging that non-stretchy fabrics, so I strongly advise you to get more yellow than you need and practice, a lot. The one you linked was very clean, therefore I suspect they did it by hand.
You can paint stretchy fabrics a bit easier than sewing, but both processes require stretching the fabric base while you work. If you opt to paint, you will have to do two coats of paint, I'd do white first, then yellow over the white. Otherwise getting yellow to show up on black will take 6 or 7 coats of paint.