gtk:rgb-to-hsv (r g b)

r -- a number coerced to a single float for the red component
g -- a number coerced to a single float for the green component
b -- a number coerced to a single float for the blue component
h -- a single float for the hue component
s -- a single float for the saturation component
v -- a single float for the value component

Converts a color from RGB space to HSV. Input values must be in the [0.0, 1.0] range. Output values will be in the same range.