i know what he means.
in a orangey warm setting at night OUTDOORS, say with a warm building as background (say 50-100m away), you shoot subject with flash. so subject becomes ghostly white (ethereal looking) compared to VERY warm background.
another case is when background is lighted by orangey street lamps.
adjusting white balance does not work because your subject is cool, and background is warm.
seems like a flash filter is the only way, have not tried it out though. anyone has better knowledge or ideas?