[CW]

I am no expert on comic art or Schulz, but based on the bottom plate ("The Bridge Girls"), this seems more to me like a framed memento that 4 good friends put together for fun using a comic strip that had a bridge reference.

The cut piece looks to be on standard newspaper stock, and the color differences could just be because the online version was retouched for better color compared to what was used for actual printing in '98, or the yellow faded due to light exposure.

From the few pieces I've viewed on Heritage over the years, most original art or production pieces are done on bristol board or a thicker medium than what you have there. Again, not an expert, but those are just my initial impressions.