prolog:line_editor_attributes/2

prolog:line_editor_attributes(+Off, +On) is det[multifile, library(editline)]: Tell libedit how to switch the decoration of the line being edited off and on again. The toplevel leaves the attributes of the colour class input in effect while the user is typing (see decorate_prompt/2 in boot/toplevel.pl). Erasing part of the screen paints it with the current background colour, so libedit must switch these attributes off before it erases the rows the line no longer uses, e.g. after unwrapping a long line or moving from a multi-line history entry to a shorter one. See EL_ATTRS in libedit.
The toplevel calls this each time it builds a prompt, so a theme loaded at run time is picked up. Does nothing if libedit is too old to support this.