Elisa uses the color scheme's highlighted text color for headerbar labels. This is not
semantically correct since this color relies on being above the color scheme's highlight
color to ensure adequate contrast. However the headerbar's blur does not do this; rather,
it always produces a dark-ish color. This causes issues for color schemes where the
highlight is light and the highlightext text color is dark, such as Materia Light.
This patch fixes the problem by always using a hardcoded white color, which always looks
good against the dark-ish blurry headerbar.
BUG: 410560