The German cockroach is omnivorous, eating a wide range of human foods, pet food, fruit, leather, and even book bindings.
In the bathroom, they may eat: toilet paper, soap residue, used diapers, trash, and toothpaste. [1]
They respond to two regions of the spectrum — 490nm, the blue-green area, and 365nm, known as the UV-A region.
I'm guessing they won't respond to the red-ish region of humans' visible spectrum.