I don't know the answer, but I do know that last summer I hadn't used the program for quite some time (several months) but when I did several of my imported planes were all white.
I was able to delete them and load new ones with no problem.
If you learn how the system works you can create one any color scheme you want, or just edit what's there. I've downloaded the electric version, it is a very pleasant flyer.
It is just the way Steam works. I have more than one game thru Steam. Mine is set to update as the PC is warming up/loading. Then whenever you click on a Steam related item you don't have to wait.
I have 9.5 and Malwarebytes and have no problem downloading aircraft. It must be some other setting in your computer rather than the game program. I'm also playing through Steam rather than a disc, But that shouldn't matter.
I believe it is part of the change of ownership. They are probably wishing to update their database with new product key #s. The upgrade is I assume an enticement to log in and make the change. Also by promoting usage of Steam the production cost are slashed dramatically. I've been running mine...