gtk:rgb-to-hsv (r g b)

r -- a number coerced to a float with the red component
g -- a number coerced to a float with the green component
b -- a number coerced to a float with the blue component

h -- a float with the hue component
s -- a float with the saturation component
v -- a float with 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.