This quick mockup shows an un-focused matrix with the current selected track cells in a different shape.
Could be optional:
Attachment 835 not found.
Also the cells with no pattern data have a ghost shape for same indication.
EDIT: even in the forum friendly shrunk size you can spot the selected track 
836 
edit: with selection borders.
I must admit I’m not to fond of your mock up and used shape, whats wrong with how it is done now? I can only see benefit in making the current selection borders more brighter.
I have to admit that it is not the prettiest in the world, 
but I am all for better/ more obvious selection, particularly when you can have independently horizontally scrolling pattern editor and matrix now. This makes relative postion of the two cursors change quickly.