The first Sonic Boom shirt to appear, is this long sleeve one in December of 2014. It has a mottled gray short sleeve, with red long undersleeve. Sonic, Tails & Knuckles are all in CG, in a screen-tone dots background circle with the logo at the bottom. "Gotta Go Fast!" is written in gray above them.
Why?
Because a designer "looked at the internet" and stole a meme without knowing anything about it. "GTG Fast" makes fun of Sonic X - it has nothing to do with Boom. The portrait of STK looks good, with friendly Sonic, winking Tails &...standing there Knuckles? At least the design is pretty fresh.
This is a JC Penny item, in the boys/teens area. It should be between 8 and 10 dollars, depending on any sales they may be having. It has no paper tag, but the Boom logo is in the collar.