Jeans which are Blue. By 'Jeans' I mean denim trousers (they're all the rage with the kids these days) and by blue I mean one of the shorter wavelengths of visible light near the higher end of the visual spectrum, next to violet.
The general words I've heard is the genre started with Mister Levi Strauss during the California Gold Rush. Cotton weave trousers would not hold up very well the the physicial labour the miners were akin too, so the 'pants' would have to be either patched repeatedly or replaced on a regular basis. In comes Levi, with trousers made of cotton but woven so it was as strong as steel -- you could punish then far longer then your could regular cotton and the fabric took patches better.
I would describe what they look like here, but if you're reading this, hell, you're probably wearing a pair right now.