Last year my husband and I thought we were being very clever by painting our dog instead of getting a costume. He's a white german shepherd, so we painted black stripes on him to make him into a zebra for this pet halloween contest. And actually a lot of people didn't know he was in costume and thought those were his real markings and asked us what kind of rare wolf is he...? We didn't come close to winning anything in the costume contest. The winner was a "little red riding hood" dog.
Then, after the costume contest, we tried to wash off the paint...and to our horror it didn't come off! So we took him to the groomers. He was there for 6 hours, and they still couldn't wash off all the paint, there were gray streaks left. They demanded I bring in the paint to show them. It was just stage makeup that we got at the local department store in the halloween costume section. It said on the box that it was water soluble....I had three groomers crowding round me shaking their fingers accusingly at me, they said you are not supposed to use human paint on a dog, if you want to paint your dog apparently there are dog-specific paints and dyes, and they brought out a bottle to show me!! I didn't know that!! So anyway, they said the residual gray streaks would just have to wear off over time. It was TWO MONTHS before the last of the gray streaks finally wore off! In the meantime, every week at the dog park at least one person would come up and ask me "what kind of dog do you have, I've never seen such unusual markings..." One person even insisted that my dog was some rare european wolf-hybrid which he claimed to have seen before....!!
This year we didn't do anything for halloween.