Not all cancerous or non-cancerous moles present identically. Because the appearance varies, you should have any new moles or changes in existing moles screened. Typically, however, cancerous moles may have an irregular border with ragged edges. The color may be irregular, with shades ranging from black, brown, and tan to white, grey, red, pink, or blue. Ultimately, you cannot tell if a mole is cancerous by looking at it.