[FFmpeg-user] Decoder flag "gray" seem to not work

[Andrey Utkin]

This flag seems to be used in sources for mpeg4video and h264, but i
cannot see its effect:
By ffplay:

ffplay -flags gray -i
http://download.blender.org/peach/bigbuckbunny_movies/big_buck_bunny_480p_surround-fix.avi

ffplay -flags gray -i
http://ftp.nluug.nl/pub/graphics/blender/demo/movies/Sintel.2010.720p.mkv

By ffmpeg with reencoding:
ffmpeg -flags gray -i
http://download.blender.org/peach/bigbuckbunny_movies/big_buck_bunny_480p_surround-fix.avi
-vcodec libx264 -f mpegts - | ffplay -

ffmpeg -flags gray -i
http://ftp.nluug.nl/pub/graphics/blender/demo/movies/Sintel.2010.720p.mkv
-vcodec libx264 -f mpegts - | ffplay -

Any ideas?
Is this option broken, or does it work another way, or do i do something wrong?
-- 
Andrey Utkin