Here's a green tee starring...Froggy?
Big the Cat's pet frog most known for accidentally eating a chaos emerald in Sonic Adventure 1 gets a solo shirt, against most of the odds here.
The light green tee has a large red shaded heart, and in the middle of the heart is a large full color art of Froggy. Is the frog cute? Is the red an ideal background for the green color? Are you Big the cat? Some of these are easier to answer than others, but regardless of the answer, this shirt is a real item in the Sega Shop in 2019, and it was made for Team Sonic Racing the game. (Though, it is almost 'secretly-Sonic')

The tee is a curious choice but....
It DOES come with an explanation. If you watch the little shorts Sonic 'cartoons' on Youtube, you'll find the Team Sonic Racing ad / mini-show. In it, Eggman tries to trick Big (of Team Amy) into quitting the race by putting up a "Frog Merchandise Stand" with all frog themed items. This tee, and the cap hat are among them. Wacky hi-jinx of course, ensue...but what's even wackier is that the Sega Shop decided to make the tee a real thing.

This hat is about FORTY dollars! This tee is about 23 dollars, in adult sizes.Neither one is a bargain, and if you had never seen the mini advertising cartoon for the game, you can't even get the joke. The slice of the Sonic fan population who sees the cartoon, gets the joke, then has the big dollars to spend in the store getting the gag item...can't be imagined to be very large. Is this even going to sell? Isn't the joke from the mini-show that the hat and tee are so silly & wierd that only Big the Cat would ever wear them? Even though it is explained, the whole situation remains strange. And Green. This is a 2019 item.