I’ve searched for the shirt before but never found any information about it. The folks at Secret Cinema made this replica for their production last year (not too accurate but definitely looked the part from a distance):
The beige and green shirt appears to have a seam and a distortion in the repeat in the same place as the supposed Shah shirt. Maybe the pattern is just more random than I presumed but maybe it could be a clue. I reckon that shirt could be store bought and then altered later to fit Marty's style. It also looks like what I portrayed as dots are actually tiny text. It doesn't really make sense they would cover it with the green and black rectangles so maybe those were added later.