bg = display.newRect (100,100, 300, 300)

local function listener (event)
r = math.random (1,255)
bg:setFillColor (r,r,r)
end

local function tl (event)
        if event.phase == "ended" then
                if t~=nil then
                timer.cancel (t)
                end
        local t = timer.performWithDelay(500, listener)

        end
end

bg:addEventListener ("touch", tl)