clock.lua

mon = peripheral.wrap("left")

mon.clear()
mon.setTextScale(2)

while true do
 time = os.time()
 time_str = textutils.formatTime(time)

 if time > 6 and time < 18.5 then
   mon.setTextColor(colors.yellow)
 else
   mon.setTextColor(colors.blue)
 end

 mon.setCursorPos(1,1)
 mon.clearLine()
 mon.write(time_str)

 sleep(1)
end