In this dialog you change the color of the selected image parts.
Three radio buttons control the hue setting;
Change -> change to new hue. This option is useful if the image part your editing has uniform color. Like a plain wall or something.
Shift -> shift colors. This options is useful if your image part has many different colors. Like a striped cat maybe.
Keep -> does not change the hue at all, only the saturation and value parameters are active. Useful when you only want to make use of the Object isolation functionality, or if you want to make an object more or less lighted or saturated.