I simply printed a picture of the decal from google, cut it out to make it a stencil, traced black marker around the edges, and painted from there.
Let me say, that the "real" shirts are red, with the white and black, but I could not find any red onesies and to dye ONE onesie would be crazy, but you could always do it it you wanted.
My supplies are simple and cheap. Acrylic paint in the colors and puffy paint in the matching colors.
I purchased the red and blue both paints at Michael's along with the onesies. (Michael's is a little pricey on the baby onesies, but I had a 40% off coupon which beat even Walmart prices).
Make sure you put plastic (I used grocery bag) inside the onesie to make sure the paint doesn't bleed through! :)
It turned out pretty great!
