Qt.hsva was added in Qt 5.5 and the hsvHue stuff was merged in July 2016, so should be fine to use now.
Color looks the same as before. Value needs to be [0,1] hence the +0.5 and modulo. I tried just +='ing hsvHue but that didn't work.
Btw, isn't that just inverting the color? ie. we could just 1-r, 1-g, 1-b the color?