In a move away from the bold colors of the iMac and in a return to the styling of the traditional mouse design, in 2000 Apple discontinued the USB mouse and introduced the monochromatic Pro Mouse. A similar design to the ADB II mouse, but this time in black, was surrounded by a clear plastic shell. After taking years of criticism for their continuation of the 1-button mouse, Apple effectively flipped the design of a “normal” mouse upside-down, with the sleekly featureless appearance that resulted inspiring its jocular appellation as “the first 0-button mouse.” This was the first Apple mouse to use an LED for fully solid-state optical tracking instead of a rubber ball.