Hey there! According to this wiki, Gary does - in fact- wear a green tank top. Just thought you should know :/ ibrpg.wikia.com/wiki/GarryAlso, it is a fan piece, so some alterations to a character's design shouldn't be that big of a deal. (It's not like the artist changed the entire colour scheme of the characters or anything...)
By the way, 134134* did a marvellous job on this. This 'pairing' is just so adorable! xD Keep it up!