http://doc.qt.io/qt-5/qcolor.html#the-hsl-color-model

HSL is similar to HSV. Instead of value parameter from HSV, HSL has the lightness parameter. The lightness parameter goes from black to color and from color to white. If you go outside at the night its black or dark gray. At day its colorful but if you look in a really strong light a things they are going to white and wash out.