A handful of users have reported that they find it difficult to read BlueJ's editor for various sight-related reasons; they can't read on certain background colours, struggle with light backgrounds, etc. We could either allow full customisation of BlueJ's editor colours (e.g. in a properties file; doesn't have to have a GUI interface) and/or provide a backup theme or two (e.g. "dark mode"). I think it's just the handful of scope colours and font colours that would need customising.
I note that this is partway solved for the Stride editor, which is more of a problem because by default it has coloured backgrounds throughout. Although it's clunky, you can just edit the CSS file to change the colours. (And if the Java editor ever gets rewritten into JavaFX, we would have a similar solution).