A shape and color changing controlled craft

My sister was driving us on I 90 east when we saw something flying above us. I thought at first it was a paraglider in profile, in silhouette. It was between the two sides of the mountain across the middle where the freeway runs. I couldn't tell its size or what distance away it was. It came over and around the side of the car and it appeared to be a bag, but it wasn't moving like the wind was pushing it. I couldn't see any drone frame, then it changed and looked like a purple rectangular box kite without any visible drone frame. I thought maybe it was a state patrol drone because we had just passed a vehicle that had been pulled over, but I didn't see anything other than a kite material box. I thought it was the size of a couple shoeboxes. My sister saw a bag like thing go over the top of us, that changed color from dark to purple and from a difficult to decipher shape to a bag like shape. Both of us saw it move in a controlled not natural way.