I think, for mastering purposes, it would be ideal if Renoise can show each instrument with a different color, in the spectrum analyzer.
It would make it easy to spot sounds eating eachother, so they can be adjusted, when you do mastering.
Just as an option, to turn on/off.
The freuqncy analyzer is nothing but a display of an FFT transform of the Master channel. I think the only way to implement what you are speaking of would be to analyze every channel the same way and display all af these transforms on the same screen, but I’m fairly sure this would be a display of pure chaos, since most instruments are wider in the spectrum they take than expected. Not to mention the amount of processing necessary could be high with a lot of tracks. I also don’t see how that would help you do mastering.
I think he means mixing.