I am having a weird issue with the props on the 1900C. I also have the 1900D, and it does not have this problem. It seems that all of my scenery is disappearing behind the props (Trees, buildings, clouds), leaving only the basic landscape. This is different than the solid black prop issue, as the propellers are perfectly transparent. Here are some pictures:

Part of your problem is the alpha channel, but if you're using FSX for your 1900c, the problem with missing background when looking through the spinning blade is a know issue which has no fix. This texture was originally made for FS9, and they don't work 100% in FSX the way it does in FS9.