Darkroom coat
From Silvergrain Labs
Zyrca Euro Salon Shirt, about $30. Sold at many salon supply houses, such as http://www.folica.com.
This is a very nice all-black nylon coat treated with water-repelling Teflon fabric protector. This product is sold for salon use (to avoid exposure to perm chemicals, for example), but it works great in darkroom. Long sleeves protect arms from chemical exposure but when you splash water, you can just wipe it off (the coat doesn't get wet!).
I used to get dark stains on my shirt due to splashes of fixer solution, but after started using this product, I have no problem with it.