I think that is not possible, at night, see the contrail of aircraft, as white as snow ... Unfortunately I do not know How can change, I think they should have the same rule of the color of the clouds, if the sun is now below the horizon. And they are hardly visible when the sun is below the horizon. I think it would be important to change, it is really nasty! The version of FGFs is 3.3 with an NVIDIA 870 and B757-200.