Gutenberg uses two different attributes for text colors:
* `style.color.text`, and
* `textColor`
However, the second one is used only when a color from the default
palette is selected AND the post is saved and reloaded.
With this fix we use the human readable string from the default palette
as a CSS variable.
Please note that while Gutenberg correctly assigns the appropriate CSS
class to render the right color, the problem is that if the color is
handled by a class, it can be overridden for example by themes.
See woocommerce/woocommerce-blocks#6492
7531428b31