Like Kickingfrog said, not sure if they mask or attract... but I have great results with them! I use the Fish Formula Crawfish and Shad scent on the dressed treble of the Roostertails I throw, and garlic scented Spike-it lure dye on my Sabiki rigs.
I may just be a confidence booster, but I always seem to catch more fish when I use it, than when I don't!