Nice to see how this has developed. I always wanted an onboard spectrograph - as opposed to send things to Spek.
I do have a couple questions/comments.
First, for the life of me I can't seem to figure out how to change the size of the spectrogram window. I'm not sure if its because I'm using Album Cover view (although the other views didn't work either), but as it sits right now, the window is eating up too much vertical real estate for my liking.
Second, my legend only shows up to ~13000Hz (regardless of file format). I see in other pics it does go much higher
Finally, any of the colour themes from Magma on down won't show an image - not a big deal, but I thought I'd point it out
For the record, I'm using your latest release (for .7003+), MB version 3.3.7003, and the abominable Win 10 (1809)