... are not stored in .xbm files. Background and foreground color selection is provided in order to experiment with colors for your application.
The editor can display very large .xbm files in their actual size but the maximum bitmap size that can be edited is 2500 pixels. This limit is arbitrary and can easily be changed, but bitmap edit grid loading and, in particular, garbage collection become quite slow if the limit is a lot more than 2500 pixels. The gridMax constant sets max size.