lightToDarkThreshold property
Vote fraction required to flip a control from light to dark.
A control in its light appearance flips dark only when at least this
fraction of its grid cells vote for light glyphs (dark appearance).
Together with darkToLightThreshold this forms a hysteresis band:
content sitting right at the contrast boundary cannot flap the control
back and forth. Must be within [0.5, 1.0]; defaults to 0.6.
Implementation
final double lightToDarkThreshold;