Ich isn't yellow, it's white, looks like the fish was dipped in salt. If this is a yellow-goldish sheen, it may be velvet, another parasite. Check here:
Edit: Yes, ich is contagious, as are most fish parasites. Treatment is required for the fish to fully recover and kill the parasite. A full treatment regimen involved several weeks of treatment, as the parasites life cycle can take several weeks to complete. Any spores left in the substrate will then hatch, and re-infect the fish. There are lots of options, I favor heat and salt. But, as always, closely diagnose the problem before treating. Could just be a color change on the fish, no problem at all!