Everyone knows about the spines on cacti and the thorns on roses, not to mention the claws on cats and the spikes on porcupines. Many plants and animals also produce poisons and irritants which drop them down to second or third on everybody else's shopping lists. One of the most interesting ways that animals control their interactions is through coloration. Then there are the sneaky ones who take advantage of someone else's coloration defense. Camouflage is a coloration pattern designed to hide the presence of the organism.
Some organisms simply match the backgrounds of their normal habitats.
For example, the overwhelming majority of wild gerbils are brown just like the dirt they hide against. Some organisms, like the chameleon, can actually adjust their body color to a certain extent. There are other coloration mechanisms which hide creatures. For instance, some animals are colored in irregular or confusing patterns which tend to make the body outline hard to distinguish, thus confusing predators. Zebras seem to be pretty obviously colored, until you see a herd of them all running and jumbling together.