marlin....I've always wonderd about the Tamarak's as well.  Some years they come on in color while there's still alittle deciduous color remaining as well....often they seem to turn yellow just after the deciduous drop...and sometimes they seem to hang on into Nov.

This last fall, I noticed a short season for the Larch color, and most were bare Nov 10th.  Thought it was a pretty poor intensity of color as well.  I love to photograph them.

So what prompts them?....same as the other trees....light, temps, and the years water availability?  It seems to me that dry years seem to produce a shorter color show....but by my (admittedly poor observational skills)...as much more intense color show.