The Pinches Wall topo, printed upside down and elongated on the front of of the T' shirt, for easy reading.
or his other idea: simply an 18% grey rectangle on the front for all the photographers out there. obviously on a green/yellow/blue t-shirt.
or hows about some tiny text on the back saying "if you can read this you're spotting too closely"?
nah, he means those colours on the same shirt, like this:
Fake chalk hand prints on the back in a similar theme?