At 1991 triangular bright yellow colored objects on black sky in central Greece,EU.

The event took place in summer of 1991 at night around 22.00 - 23.00 local time.
I live in central Greece, SE Europe.
 The objects had triangular shapes with bright yellow color in a black sky.
they went straight and suddenly changed their track and again straight.
They moved like a saucer so you could see the angles of the triangles to change continuously their position. After some time they disappeared...
 I was 12 yrs old at that time and was with mother and friends in central square of the city.
 Many regions in greece had seen such objects at that time and a local newspaper had written that the regions match the air corridors of an emergency situation N.A.T.O. would use from bases in Italy and Germany. At that time was the crisis in Iraq.
Maybe secret weapons / technology???  I am 25 yrs old, University graduate and just finished my military service in the navy (compulsory here for 1 year)
Date is approximate.  PD