Problem with HSV and RGB color model

1. Why use HSV instead of RGB?
2. Why RGB is a poor choice of feature space for object recognition?
3. How could using the RGB colour space be problematic?

Why use HSV instead of RGB?

The HSV color space (hue, saturation, value) is often used by people who are selecting colors (e.g., of paints or inks) from a color wheel or palette, because it corresponds better to how people experience color than the RGB color space does.

Why RGB is a poor choice of feature space for object recognition?

Object representations based on just RGB data are sensitive to illuminations and shadows. Moreover, they cannot provide accurate representations of the shape of objects.

How could using the RGB colour space be problematic?

If you want to do something meaningful with colors, don't use RGB, and don't use HSL (which is based on RGB). These spaces are problematic. For instance, pure blue and pure green in RGB space have very different lightness.