I'll definitely look into making some, you're not the first person to ask about blindfolded shirts. I'll try and get some more done this week although I'm quite busy atm so I'll see what I can do.
If anyone else has any ideas (as well as yours above) for a good blindsolving t-shirt then I'd love to hear them.
Recognizing that I am utterly incompetent when it comes to anything creative or involving design AND that I slapped these together in MS Paint in about 2 minutes, I came up with a couple different layouts:
I've added a dark gray colour and some other ones to the 4x4 shirt and changed the design. I had to add it as a new product as you can't edit existing ones. I can add other colours to the other ones as well but don't know if I'll do it yet.
Here is the dark gray and charcoal colours. I do think this design looks better now as well.