The new beetle has tan wings and a light brown head. They darken with age until they are black and look much like a common water beetle. But even if you keep adding food, they bin will eventually become contaminated with fecal material, so you should empty it and start off fresh. Doing this, you would lose thousands of eggs and tiny worms. I've read that you need a minimum of three bins to make this work.
Temperature plays a big role.
80 degrees is optimum. At lower temperatures, the whole process simply slows down, and as you probably know, at refridgerator temps, they worms go dormant. I put 5,000 worms in the bin and have fed less then half to the blues. I've read that 50 beetles will yield 3,000 worms in 3 months. Search past posts - there are some good links on raising mealworms.