Clearly a mistaken fashion trend, salmon panties indicate a complete lack of originality, and a vain attempt to look metrosexual and/or look like one is transcending gender stereotypes regarding colours. In the end, it probably has nothing to do with either, and more to do with a need to conform to jockhole norms.
Steve: "Shut up, man. I'm too busy checking out blondie over there. Stop looking at guys"