This large demonstration uses hydrogen peroxide (H2O2), sodium iodide (NaI) and soap. First we pour in the hydrogen peroxide, then the soap and finally the sodium iodide disolved in water.
The hydrogen peroxide used in the demonstration is 30% hydrogen peroxide. The 30% hydrogen peroxide is not something you would put on a cut or scrape, but it works perfectly for this demonstration. The sodium iodide reacts with the hydrogen peroxide (H2O2) by removing an oxygen atom. This essentially produces water and oxygen gas (H2O + O2).
The oxygen gas produced gets trapped in the soap which produces the big ball of foam. The reaction produces oxygen gas, water and iodine. That is why the foam has a yellow color. If you were to touch this foam, your hand would be stained yellow just as if you put iodine on your skin.