Mine

package require Tk

pack [button .b -text "Porco Dio" \
    -command {.b configure \
        -text "Sempre sia porcato" \
        -command exit}]
pack [canvas .c -width 300 -height 300]

foreach {x y} {0 0 0 1 0 2 1 0 1 1 1 2 2 0 2 1 2 2} {
    .c create rectangle \
        [expr $x*100] [expr $y*100] [expr ($x+1)*100] [expr ($y+1)*100] \
        -tags _${x}${y} -outline {}
}

proc x {} {
    set rand {}
    foreach max {3 3 256 256 256} {
        lappend rand [expr int(rand()*$max)]
    }
    lassign $rand x y r g b
    .c itemconfigure _${x}${y} -fill [format #%02x%02x%02x $r $g $b]
    after 50 x
}

x