This is Gap's Dip-Dyed Summer T (style #655031), which retails for $18.50. (At the time of this review, Gap is running a promotion on "Summer Deals", and this tee is on sale for $15.) This tee is available in petite and tall (only petite is showing up right now), and is available in a few different colors, but only cocoa is showing up online. [You will probably have better luck in-store for this tee.] Gap describes the tee as such:
Look no further for the perfect warm weather T. Ours is light and irresistibly soft to the touch--plus it comes in a rainbow of saturated shades. Each one has a unique personality thanks to the cool ombre effect.
The fabric on this tee is a slightly coarser cotton (a slub cotton, they say), but it is not rough or uncomfortable. There is a bit of stretch in this tee, and it is a bit clingy, so if there are any problem areas (especially in the middle) that you want to hide, this tee is probably not the best candidate for the job.