Fortunately there is no rust. The inside case is painted red, you might be seeing reflections. Tractor is stored indoors and the shifter is a cable shifter, located up on the fender.There is rust on the gear in one of the pictures and the transmission oil looks like it's starting to get milky. You drained the oil which is good. I wouldn't reuse it. Also if your shifters are on the top of the transmission housing make sure the rubber boots are in good shape as that's usually the first place for water to get in if the tractor is stored outside.