I have a purpleish black little spot its not a mole nor a bump jst a spot on my back could it be a sign of something serious?

See a dermatologist: I am always concerned about skin lesions and moles that are 1) black, grey, or blue, 2) made up of many colors, 3) have irregular borders, or are bigger than the size of a pencil eraser. I am also concerned about moles that itch or bleed spontaneously. Please have yourself checked by your doctor; a dermatology evaluation may be in order.