For the blue and violet noise, I took the pink and brown noise respectively and subtracted the offsets instead of adding them. When I eyeball the frequency spectrum of the resulting outputs it looks correct to me, i.e. the blue graph appears to be a mirror image of the pink, and the same can be said of the violet and the brown. I did not do anything else to confirm the correctness.
6e15607 avfilter: Add blue and violet noise generation filters
doc/filters.texi | 4 +--
libavfilter/asrc_anoisesrc.c | 72 +++++++++++++++++++++++++++++++++-----------
2 files changed, 57 insertions(+), 19 deletions(-)