I agree with shotandshell. With brass there isn't much to worry about other than color change. If you ran it a very long time it tends to give it a shiny look which is what you see on the marsh shells that are run for extended periods. For short runs there is not much change. Copper is about the same other than it is much quicker to get a coppery look but a short run of a couple days to a week won't have much affect. But the important thing here is how 'hot' you run it. If run at 5 to 10 amps or more, the time to see an effect is much quicker. If run at a low amperage (0.5 to 1) it takes a little longer to clean but there is less effect on the brass and copper. If the brass or copper has any patina on it the electrolysis will tend to darken that patina and after running in electrolysis you can scrub it off and get the bright metal look although I think most people tend to leave the darker look.
The white metals are a little different issue. The white patina you see is often pretty deep on them tot he point of being called corrosion so the electrolysis will break that down just like it does on the iron. So generally I leave that out of the water except for common Parrott fuses not in good shape. But even on them if the condition is decent I'll leave that out of the water and do a little hand cleaning after electrolysis to help it out. And like the copper and brass, running a low amperages is the recommended way and will have less effect on the white metal if you do put it under water.