The audio mixer is completely user-unfriendly when one has dozens of inputs and 2 or more buses.
Using more colors would improve usability greatly.

i.e.: keep current green for active "M" (master) icon;
use a different color (i.e. light red) for active "A" (bus A) icon.
After a few buses, maybe colors run out but most users will not use more than e.g. 4 buses.

The Solo (S) button should not be green (very confusing now), but orange.