I was attending an outdoor concert at tanglewood in lenox, ma. i had noticed various aircraft throughout the evening at high altitude with flashing strobes, etc. point of interest, i grew up around naval air stations and air force bases most of my life, and am extremely familiar with numerous aircraft and aircraft types. i happened to notice some movement overhead, and was surprised to see 3 teal colored objects in a perfect triangle formation. the color was kind of a dull colored teal, not overly bright. they began accelerating rather quickly and then disappeared into some cloud cover. no strobes at all and they were absolutely and completely silent. all 3 objects accelerated together at a surprising speed, all the while maintaining the perfect triangle formation. total observation time was only 5 or 6 seconds, but it was enough to unnerve me a little bit. while i have believed in ufos for a very long time, and know some people who had seen some before, this was the first time i have seen any. i have f-15 eagles, c-5 galaxys, c-130s, chinooks, blackhawks, hueys and other aircraft fly over my home several times a week, at all hours, sometimes quite low and loudly, as i live between the westover afb and the barnes afb. but this was not something of ours. the precision of the formation, and the coordination of the acceleration, was absolutely perfect, and something we are not able to do. not like this. and all without making sound. again, it was a bit unnerving.