I cannot find this dress on Gap's website, but I'm pretty sure it is style #655030. It is alpha-sized, and retailed for $39.50. It was available in a number of saturated colors, including bright pink and bright blue. This is a rich, purple color in size small.
I was tempted to pick this one up, on more than one occasion. The first time I tried it on, and another time I almost grabbed it in the pink color, but I resisted both times.