If you use the licensed patterns, the colors and cut will be indistinguishable from the commercial ones, but yours will look nicer because your fabrics will be better quality, and presumably the fit and finishing will also be better.
I made costumes for years for the little girls of my acquaintance. Here's a tip: if you want really good comfort in the parks, go to a linens dept. and buy a king-size high-thread-count sateen sheet for your costume fabric (if you can get it in the color you wish to have; Snow White can be difficult in this respect, as the dress is a bit garish.) Sateen is very comfortable and washes well, but still has that sheen that little girls need for it to be special. Good sateen won't be cheap, but if you know the dress will be worn to death, it is worth it.