ubuntu 18.04 LTS
ppa:ubuntuhandbook1/audacity
2.3.3
Light
also grayscale version of spectrogram - white - currently does not go to 255 but 192
isn’t theme-settable (e.g. black-white invert for dark themes)
Built-in Light Theme - Button Corners Black instead of transparent
Looks fine here in the version that I built from the source code:
The reason that your version does not have transparent corners is probably due to how the PPA version has been built (which library versions they use).
Yes, that’s because the spectrogram is overlaid on a grey background. There is a longstanding feature request to extend the grayscale contrast, but to date, no developer has picked that up. It is intended that track colors will eventually be fully customizable, but it’ll be a while before that happens. It is not scheduled for the next release.