Just in case you've been spared the sight of those long-johns, they're washed out pale green y-fronts with elastic leggings attached to them.
They look like something found at the bottom of a spare PE kit box, and we were told by the QM that they were only used for Kermit the Frog parties and "If you wear them you're SAD!"
We called one of the watch officers that, on my last ship. Looked like something straight out of Sesame Street. I mean, it was literally one eyebrow! Weird!