hzvToRGB = function hzvToRGB(hue, zest, val) {
                if (hue < 0) {
                  // Hue must wrap to allow projection onto red and blue.
                  hue += 6;
                } else if (hue >= 6) {
                  hue -= 6;
                }
                if (hue < 1) {
                  // Red to yellow (increasing green).
                  return zest + (val - zest) * hue;
                } else if (hue < 3) {
                  // Yellow to cyan (greatest green).
                  return val;
                } else if (hue < 4) {
                  // Cyan to blue (decreasing green).
                  return zest + (val - zest) * (4 - hue);
                } else {
                  // Blue to red (least green).
                  return zest;
                }
              }
Convert an RGBA array to HSBA.