There's a fuel filter internal to the fuel pump (inside the tank). Don't worry about it unless you're having a problem.
FWIW, diesel pumps aren't necessarily a pre-determined color in any given state. In WI, they vary, Yellow, Black, Green. Size will also differ depending on where the pump is. If it's a truck pump, it will be a stand-alone pump and the nozzle size will be huge. If it's a car pump, the nozzle size will be the same.
Where you WILL be able to notice is that typically the diesel pump handle is VERY greasy looking and feeling. Diesel doesn't evaporate like gas does, so it gets messy...