As Ed said, the shirts are plain white. We did them on our trip in August of 2016. Our Mickey's turned out okay, but I had hoped that the colors would have been a bit more "Vibrant". Still, it was a fun activity and my DD11 had an awesome time doing it.
I did one too. I did buy their shirt, but the funny thing is that the gloves they give you were just WAY to small for my hands. They give you, basically, the plastic Food Service type gloves. For me, they had to go get some larger latex (like medical) gloves to fit my hands.
All in all though, we felt it was a worthwhile event for us.