Large, low craft that slowly approached over top of the trees, then hovered for 20 minutes

We saw a light approaching from a distance.  We thought it was a lone street lamp on abandoned property.  The light moved with us as we walked southbound then it started to approached us heading west when we stopped to watch.  The object appeared above the tree line toward us then just hovered.  
I can't remember how long we stood there, maybe 20 minutes.  The craft was very large, say 2 football fields and was just above the trees.  The bottom of the craft had a number of small colored lights, like an electronic board would have.  Several white, amber, some red and then a few green and blue.  
The only other description would be like an engine.  There was no noise when it approached. Only a beam of light on the approaching side of the craft leading down to the ground.  We could see it but, that light never passed over us.  
We wanted to run but, it was so large, I said, "where?" Just then, it took off with a blink of an eye.  We ran home, called airports, TV! stations, newspapers, no one else reported the sighting.  I ran into the person I was with that evening several years later and we talked about it again.  It had been so long without discussing the sighting that I wanted to make sure it wasn't a dream...it wasn't. 
I never had an interest in it before but can say the event changed my life profoundly.
Witness indicates that the date of the sighting is approximate.  PD