That was one issue that bothered me so much in Cubase, it was one of the reasons I didn't go forward with it.
But in S1, It seems logical to me. Red is universally known as "Stop" or danger. In this case the audio in this track is "stopped".
Green for solo is not a bad idea. I see where you are coming from but yellow is a color universally used to highlight text to get one's attention. In this case, to me, it highlights the tracks that are being played.