Sphere shaped UFO that disappeared and gave off strange visual effectsI was in the parking lot of the medical center in Vail where I work. A man and his young son had exited the building and let a group of helium filled balloons go. I watched the balloons drift to the west with the parking lot attendant, who after a few minutes turned away. I continued to watch the balloons when I saw a round sphere shaped object appear to the left of the balloons. The sphere had sharply defined edges and appeared translucent and seemed to turn various shades of grey. It began to move in an arc downward and to the right, as if circling the balloons. I called the parking attendant to come and see this but before he returned the sphere, after completing a quarter circle and being below the balloons, simply vanished.What happened next was strange in that both the attendant and myself had this unusual visual effect like hundreds of bright particles flashing around in front of our eyes. The attendant described it like crystals shooting about. This effect continued for 4-5 minutes before it began to dissapate. I am a field investigator for MUFON and have had several sightings in the past where the UFO disappeared and I have seen this same visual effect. I filed a report with MUFON on this sighting.((NUFORC Note: We express our gratitude to the source of the report, and to MUFON COLORADO for sharing the information with NUFORC. PD))