Ssgardener, I think why [that] Bob suggested the darker color (please yell if I'm wrong, Bob #1!) is that there are different strains of Heuchera, and there is one - H. villosa - that does better in the heat/ humidity than others, being a native of the SE U.S.. It is also the parent of many of the new Heucheras and probably Heucherellas, you just have to watch which type you get.
