Now I am no expert on radar meteorology so feel free to correct me if I am wrong but, the reason for the orange and red and even purple echoes is because the radar is probably in what's called "Clear air mode." There are two main modes that radars can go in. One being clear air mode and the other being precipitation mode. Clear air mode is much more sensitive, hence the darker colors. When in clear air mode you can pick up things such as a flock of birds going by. In precipitation mode, the radar is for the most part only showing where heavier bands of precip is. Although, it is not guaranteed that the precip is hitting the ground....thats another story.
One other tid bit, if you go to the NWS site and look at the different radars you can choose between base reflectivity or composite reflectivity. From my understanding, if you choose composite relfectivity you can get a better understanding of how high some clouds are, even though the radar does not show cloud coverage. The base reflectivity scans the area at one angle, while the composite reflectivity scans at multiple angles, allowing you to see some precip that might not be at the ground yet but is aloft. If you have echoe returns in your area, you might notice a difference in what the composite reflectivity and base reflectivity are showing.
Like I said earlier, I might be wrong on some of that but, I do believe it to be correct.
Ciao,
Andy