BAM already provided an interface to configure the TiddlyWiki "Code Mirror" plugin. (Done via the "IDE Config" window, accessed via "Tools", and the "IDE Config" item within the "BAM Customization" menu items group.

Now the IDE Config also provides an interface to change BAM's Colour Theme.

There are 19 themes to choose from. (Although all 19 can be edited, and you can create your own from copies of the existing ones, I recommend holding off on editing them until I can document which subset of the overwhelming number of colour settings actually apply to BAM. Also, I eventually want to set things up so that you can easily copy any theme you have altered to other BAM instances, as part of upgrading BAM, etc.)

Here are some examples, without altering the code mirror editor:

The Default theme:

Contrast (Dark) Theme:

Desert Sand Theme:

Gruvbox Dark Theme:

Nord Theme: