Some dahlias seem to vary quite a bit depending on their environment. A hotter sunnier growing season can really change the colors. Some just have a lot of variation no matter what - Like Holly Hill 6 in 1, which rarely puts out two flowers that look the same. And others have a tendency to sport back to a genetic parent.
It keeps it interesting.
Show and Tell is a dahlia I saw at the MN Dahlia Society show a couple of years ago and fell in love with. I have it coming this year too, and hope mine is as nice as the ones I saw.