Great tool! I was a bit confused at first what was going on, especially when I clicked on an instrument. I think part of the disconnect is that the instruments are squares in a grid, but you see oval shapes in the sequencer itself. It may make more sense to show them as rounded rectangles in the sequencer so it's more obvious that each instrument maps to a colored shape in the sequence.

The interface is also begging to be used in both directions: it feels like I should be able to click on a square in the sequencer and see the instruments light up on the right, so that I can change multiple instruments at a time for a given square!