gistfile1.txt

(START)
    @SCREEN
    D=A

    @cur
    M=D // Sets CUR to SCREEN

    (LOOP)
        @KBD // read from keyboard, 0=nothing pressed
        D=M
        @BLACK
        D;JNE // key is pressed, use black

        // White
        @color
        M=0
        @DRAW
        0;JMP

        (BLACK)
            @color
            M=-1
        (END)

        (DRAW)
        @color
        D=M

        @cur
        A=M
        M=D
        @cur
        M=M+1


        @cur
        D=M
        @24576
        D=A-D
        @START
        D;JEQ

        @LOOP
        0;JMP
    (END)
(END)