Here is the link to the Elmer's Glue shifts (or flour/water shirts). The original craft calls for flour/water, but I just use Elmer's washable school glue and it all washes right out.
Here are pics of the two versions I've made for past WDW trips.
http://www.disboards.com/showthread.php?t=1387362
June trip // Boys = Green // Girl = Pink
Halloween Trip orange/black
I couldn't find black spray-style paint so I bought regular fabric paint and spritzed the best I could. It ended up more like an 80's paint splatter style, but still cute.