What is the meaning of the color on the speed value?

In challenge mode, the video playback speed is adjusted according to your speed, relative to that of the contributor, to keep the video and GPS track in sync throughout your training session.

Here is how we use proper color to understand your training session :

Speed in green: you are driving as fast or faster than the contributor on this part of the video. The video playback is then accelerated and you can confirm it with the 'play' pictogram which will turn into a 'fast forward' pictogram.

Speed in orange: you are driving slower than the contributor on this part of the video. The video playback is then slowed down and you can see the 'play' pictogram turn into a 'pause' pictogram. 
The speed can, therefore, change from green to orange and vice versa throughout the video, as we compare the contributor's speed with your own speed on the same portion of the track.