I did not burnish, which would have caused more color variation. I did a trial patch which I burnished, but it looked really terrible. I tried with the plaster tools, sandpaper, and with a stainless steel trowel. Beware using regular stainless steel with the venetian plaster, because it leaves dark marks. I guess that is why the venetian plaster tools are all made from some kind of blue steel. The burnished portion that I tried did not look like any of the pictures of venetian plaster that I have seen, and I'm not sure what I may have done wrong. It looked really streaky and harsh, not at all marble-like.
Valspar makes a protective coat for the plaster, but I did not use it. I bought some, and tested it out. I think it is intended for walls that would not be washed frequently, because when I tried washing the area where I used the Valspar protective coating, the water soaked through the finish and some plaster rubbed off as well. Instead, I used Seal-Krete high gloss Showroom Finish, which is a concrete floor coating. I can wash the wall, and the plaster is not affected. It also made the plaster nice and shiny.
I have had two problems with the plaster. First, a piece chipped off behind the sink. I think perhaps a utensil may have gouged the wall. I tried several times to patch the spot (I have plenty of leftover plaster and seal-krete), but there was no way to make it look nice. It was always an obvious and ugly patch spot. This may be where more variation in color would have been good, because maybe it would be easier to conceal patch spots. Eventually I gave up and we put up a stainless steel backsplash. There is a picture and description of that here: http://uniquekitchenideas.blogspot.com/2011/09/kitchen-overview-east-wall-stainless.html
Below you can see the second problem I have had with the venetian plaster backsplash. There is a bump in the wall. I suspect it is a drywall screw that somehow decided to back out. I've got 2 pictures below, the bottom one is a close-up. I have no idea what to do to fix this. I have already determined that a patch will not work, so I can't chip away at it and put the screw back in. It's also not really in a nice spot to put another stainless backsplash in. It's pretty close to the sink, under the paper towel dispenser. For now, I just put something in front of that spot to hide it.