The white shirt will probably (I don't know the reflectivity of white cotton in the UV) reflect more UV than the green one, but that which remains will be absorbed by the green dyes but not the white fabric.

Respectfully,

Jerry

When I was younger, I spent an August day outside (not in the tropics, but in central Minnesota) wearing an ordinary white cotton T-shirt. I got 2nd degree burns over my entire shoulder area that required a doctors visit. I still have some scarring from that. Now when prairie-walking I generally wear a wide brim hat, and T-shirt with a loose shirt on over it.