I don't consider heucheras to be shade plants at all, except for those with very light lime or gold colored foliage that may be subject to scorch. Most display their best coloring in a good deal of sun. And in my experience, even the peach/caramel/amber colored cultivars will have very little green on them even in very heavy shade. I am not at all sure yours were labeled correctly for that sort of coloring. And the dry, brown leaves at the base are not technically a "color change" but just an indication of overly dry soil.

I've grown them for many years. Had them in many different growing conditions....sunny beds to shade beds. Mine do best in my zone 5/6 beds in beds that are shaded, or only filtered sunlight for optimal foliage color and overall health of plant.

I do however agree with the above statement that the soil may be too dry. Also adding a little organic matter {like bone meal} to the soil to give a boost in overall health.