visible whitespace config

[ChrisF]

It would be nice (and maybe not too hard, depending on how you are lexing the code), to have a configuration parameter to alter the colour of the whitespace glyphs when they are visible.

My personal preference is to have visible-whitespace on, but set it to a very light gray, but there is not a colour/font option for this.

[Darryl]

Thanks for the suggestion.

REF: 18238