Remco made some excellent space toys, including a number of space phones, an amazing B9 Robot from the TV series Lost In Space, and, of course, ray guns. The company was good at providing bells and whistles -- and lights and buzzers and whatever other battery-operated doo-dads you could imagine. In this case, the Electronic Space Gun fired a beam of light while a buzzer sounded. The red dial on the side, up near the barrel, turned a color wheel which could shift the light from white to red to green to blue. A compass towards the rear of the gun helped keep Junior Spacemen from getting lost (as long as they were on Earth, that is).
I'll admit, it took a while for me to appreciate this gun. It's angular shape looked just a bit too functional; I kind of felt like it was lacking in fantasy. But over time, I began looking at it like a prop from a space movie or something. The factors that turned me off became more appealing. Eventually, I was scouring eBay for a nice, boxed example.
Remco made a number of different variations of the Electronic Space Gun. All used the same body, but the company sometimes replaced the compass in the back with a small, spiral color wheel. The toy was released in a variety of colors, including black, red, yellow, and blue. There are also at least three boxes; this is the most elaborate. One version is also known as the Jupiter Gun, though aside from the awesome name, there doesn't seem to be much difference.