Adult lice and nymphs (baby lice) are grayish white or tan in color. If you look at an adult louse (see lice pictures), you may be able to see its abdomen filled with the red human blood it has been feeding on.
Lice eggs (called nits) look like tiny yellow, tan or brown dots before they hatch. If you pull one off the hair, it may look like a flat speck with a tiny tail (which is the residue of the hair shaft it was glued to).
After hatching, the remaining nit shell looks white or clear. It can easily be mistaken for dandruff, except it is hard to remove with your fingers.