The sky is grey.
The sky is cloudy.
The sky is overcast.
The jet is grey.
The jet is flying.
One jet is flying.
The jet is in the sky.
underside of a jet airplane 
gray fighter jet flying through the sky 
triangular shaped jet in the sky 
gray jet flying in sky 
jet flying upside down 
gray jet doing tricks 
compact aircraft with pointy nose
blank sky behind plane
The aircraft is grey. 
a gray military plane flying on the air