good to know the red over white. ;-)This is not true as stated. I have seen kayaks show up on my radar. Modern radar is extraordinarily good. Much depends upon conditions, in 5 foot seas and light rain the dinghy will not show up.
The international rules for prevention of collisions at sea (COLREGS) require display of red over white over red all-around lights, separated by 2 meters, while divers are down at night.