Generally any pattern that breaks up outlines and is even remotely colored like the environment it is in will work great.

Our brains fill many details for our vision than we take for granted. Any time that you watch magician doing sleight of hand tricks, look everywhere else but where his hands and body language want you to look and you will see how most of the tricks work. Humans are really stupid when it comes to visual distractions and we tend to only see what we expect to see in new situations.