color on B&W tvs?

[Marlin Mackley]

Hey folks, A friend told me something this weekend that rang a bell to me. Anybody remember this add? Know how they did it? :On a B&W tv she said she saw:
"It was around the mid sixties during the Tonight Show and it was a commercial for Sprite. A little multi-colored rotating flower type symbol appeared in the upper left hand corner of the screen for a few seconds(maybe 3-4). It was never shown again. The rest of the screen and ad was in black and white."

She is sure she saw it. I am guessing it would be a combination of pulsing the beam at just the right frequencies to fool the eye into thinking it was seeing color, and possibly add the power of suggestion. Anybody got any memories or ideas?
Marlin