Head lice can be seen by the naked eye but it can be very difficult. Adult lice will be the easiest to spot because they are the biggest. But at the size of a sesame seed, they still aren’t that big. Although lice vary in color, if you see a grayish-white, tan or dark bug crawling through the hair, it is probably a louse. The color of the bug depends on the age of the bug and the color of your hair. If you look closely at an adult louse, you should be able to see human blood inside it.