Stationary disk with lights circling the circumference of the object.

I have told only a select few people about this incident, but seeing that another person reported something in July of 1973 in the Oak Cliff area seems to justify this.  I was 5 years old, and my parents ran a County Home for foster children awaiting placement in homes.  My family lived in an apartment connected to the facility.  I walked out of the front door of the facility and stood on the porch.  Above me was a circular craft with lights (green, red, yellow, blue, white) circling the circumference of the vehicle.  It was not a helicopter, as the lights moved slowly around the edge.  The only noise was a low, almost muffled, humming sound from the craft.  It held its position relative to me steady, with very little side to side movement.  I was young at the time, but my memory seems to be that the craft was approximately 45 to 55 feet in diameter, hovering approximately 100 to 200 feet in the air.  I ran back inside the building and called to my father to come look at the craft, and when he and I walked back out approximately 2 to 3 minutes later, the craft was gone.  My wife and my parents are the only people who have heard that story, until now.
Date is approximate.  PD