When Tom Hanks arrived on the island, his pants were a dark green in colour. However, while on the plane prior to the crash, they clearly appeared to be light in colour. Anyone else notice this?
I just checked this on the DVD, and I think you're right. On the plane, they were khaki, but more tan. On the island, they were dark green. Not just when they were wet, but all the time.
OK. If you do not believe me you can test this out on your own. cloth of any kind gets very dark when wet. Tom Hank's character was in the ocean for several hours, and then he got dirty with being in the sand and seaweed. This is not a slip-up.
The pants probably got rather dirty. His plane just crashed, he is full of gas, sand, mud, algae, and anything else you can find in an ocean. You'd kind of have to think that his khaki pants would turn a dark green. However, I just watched the movie, and they weren't incredibly dark green, so it's possible that they are just dirty.