why colorspace value is different in different models?

I used a set of colorspace function to study the intensity of color in the same images. I had seven green colored images and I used colorspace functions like RGB and HSV. For the decreasing intensity of the green colored images the pattern of change in Green color channel was different when compared to any of the component of HSV colorspace. Is it possible? I was expecting the results in same fashion for all of the color module.

Thanks