Summer of '78, Springfield MA, a display of colors on a screen hovering above us

My teenaged friends and myself witnessed the event from the pool located on Dickinson St., Springfield, MA.  Other people present included residents of the complex.  
We were just taking advantage of their pool on a hot summer night.  What we saw looked like a movie screen shaped object, most definitely a rectangle.  It was silent, stopped above us at a height of about 2-300 feet and stayed motionless above us, but running through a number of beautiful colors.  Some of us panicked, but I was just generally curious about this event.  
After just an minute or two, it slowly and silently retreated in no particular rush.  
That's it, just a rectangular screen about 50 ft x 100 ft producing an incredible display of colors from across the spectrum.  
I was never affected physically or mentally (i hope!) and made for an interesting, once in a lifetime experience.