The general tendency (which is not the same as "an accepted approach") that I've observed in publishing over the past 30 years is toward less hyphenation of stacked adjectives, especially when one of the adjectives essentially modifies another.
If two words possess equal force as modifiers (as is the case with blue-gray in the phrase "blue-gray gnatcatcher"), it makes sense to reflect the balance between the two words by hyphenating them when they appear in combination. But if one adjective dominates the other (as is arguably the case with, say, "bluish gray clouds," where the main color of the cloud is gray but that color is tinged with blue), I don't see what you gain by including the hyphen between bluish and gray.
You can apply a similar analysis to "light brown hair" and "dark brown hair": The dominant adjective in both cases is brown, with dark or light modifying that color. Under the circumstances, it makes perfect (and consistent) sense to render the two phrases without hyphens.
As for your concern that readers might misread "light brown hair" as meaning hair that is both lightweight and brown, the absence of a comma after light signals to readers that you aren't using light in the sense of "lightweight"; after all, lightweight would modify hair, not brown, so you'd want to isolate it from brown as clearly as possible to indicate that it referred directly to hair.
None of this is graven in stone, of course. You can find lots of published instances where stacked adjectives are variously hyphenated, unhyphenated, commaed, and even slashed to serve the taste of the author, editor, or publisher. And as Robusto notes in a comment beneath your question, the whole issue is ultimately a matter of style anyway—and style rules tend to be will-o'-the-wisps.
Still, if you're looking for an approach that aims to produce results that are generally consistent and fairly rational, you could do worse than to base your hyphenation of stacked adjectives on whether the adjectives represent coequal merged qualities (as in "blue-gray gnatcatcher") or whether one adjective simply modifies the other (as in "bluish gray clouds").
Unforgiving means intolerant of any mistakes, regardless of size, reasoning, or infrequency. It is often used in contexts like yours:
http://www.dictionary.com/browse/unforgiving
It was unforgiving of him to judge the employee in such a way.
Best Answer
Perhaps a two-word phrase that aptly modifies "stability" and captures the concept succinctly i.e., DYNAMIC STABILITY