Fixed getColor method for HSV to RGB conversion

Within the method getColor for HSV colored points the following issues
have been fixed:
- conversion from HSV to RGB values
- faulty return lines
- behaviour for H values > 360 and < 0, so that the color
  gradient is continuous.

The following things have been added:
- limited s and v to [0.0,1.0], that values < 0.0 are set to 0.0 and
  values > 1.0 are set to 1.0.