If you convert (1, 0, 0) from RGB to HSV space, the result is (0, 1, 1). The output of the shader graph is expected in RGB space, so if you display the HSV output, you'll see (0, 1, 1) cyan. Normally if you need to operate in HSV space, first you convert the input to HSV, do your stuff and convert it back to RGB.
// Peter Horvath
// C4DtoA developer