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cvtColor RGB to HSV, different look???

Hello, I would like to convert a stream from my webcam to HSV colorspace.

Therefore I used cvtColor in the following code:

int main()
VideoCapture cap(0);
cout << "Capture could not be opened succesfully" << endl;
return -1;

while(char(waitKey(1)) != 'q' && cap.isOpened())
Mat frame, frame_hsv;
cap >> frame;
cvtColor(frame, frame_hsv, CV_RGB2HSV);

imshow("RGB", frame);
imshow("HSV", frame_hsv);

return 0;

First I am wondering because if I change CV_RGB2HSV to CV_BGR2HSV there is no difference in the shown images.

In the attached file you can see the output.

Why are the colors in the new "HSV-image" wrong? And what can I do to solve this?

I thougt cvtColor would calculate the matching colors for the new color space.

Thank you :-)