Phil-
Thank you for your question!
I did a little research - according the the National Severe Storms Laboratory (NSSL) - "haze, dust, moisture, raindrops and any other particles in the atmosphere will affect the color by absorbing or diffracting a portion of the white light of lightning." So, pink is just one color of lightning that can be seen.
Also, during the rare occasions when there is lightning during snowstorms (especially when the snow is really coming down hard), the lightning may appear pink - but, the snow usually makes it hard to even see the lightning, usually you just hear the thunder.
Hope this helps, and thanks for watching CBS21 News!
Paul Lynch
Meteorologist
CBS 21 News
PaulLynch@cbs21.com