If, in editing text, a Space character is used to overwrite another non-Space character, then the overwritten character is greyed out. The amount of being greyed out can be comfortably set by the user or the amount should have a good standard value.
This is a way to represent the addition of Space characters not (yet) saved.
Perhaps a better way is possible, but it seems that there must be some way to represent it other than the corresponding red hexadecimal values.