you don't need this information. Ken Rockwell just published this.
PopsHoly Cow! Color Histograms on Canon Powershots!
Reader Doug Knisely made the discovery that the Canon G12 can show RGB histograms on playback, but it's carefully hidden.
I tried this on my Canon S95, and it works perfectly!
Just press the top of the rear dial when you're seeing the monochrome histogram, and bingo!, a color histogram replaces the data display!
The hint is an [ ^ ] icon next to a histogram icon on the top left of the data screen! AHA!