(Sorry if my answer is as offensive as responding to a question about Coca-Cola with data about Pepsi!)
There are certainly some lesson plans around looking at statistics for M&M colors.
For example, see Supplemental Activity S3.3 from COMAP's "Mathematics: Modeling our World" here. COMAP (COnsortium for Mathematics and its APplications) is my general go-to for modeling related activities; for example, see the discussion of a different sugary item in my MESE post on cake-cutting.
Another brief write-up that I saw online recommended two other sources. One of these sources includes a classroom activity and has 'teaching' as a keyword; it is entitled: Testing Colour Proportions of M&Ms. The other source, The Mysterious Case of the Blue M&M's, recommends the following:
The article is from 1996, so I'm not sure if this "teaching device" is still available (though I suppose you could call and ask). You might also look up the (Landwehr et al, 1987) source mentioned at the end. Googling did not lead me to that particular one-sheet guide, though I did find yet another M&M project on the subject described online.
Lastly, you might download this thesis and search for mentions of M&Ms (e.g., p. 33, p. 243).
In response to your comment ("There are quite a few articles on using them as a method in the classroom, but I'm more interested in whether they are a useful model") I would say there are enough different items online to put something of interest together.