Change all fonts to black

I have a very straight-forward task to make all the fonts in my Vaadin app black. I tried to specify the valo variable,

$v-font-color: green;

 just to see where it changes. Unfortunately, I only noticed a single difference in the app. In my own custom style sheet I am not doing anything funny with font colors except for an icon here and there.

I dug into the SASS code and it seems like the font color is generated based on other variables I can specify. Without creating an overriding class for each and every widget in my app, or hacking the colors for other variables such as background, is there a way to get all my fonts black?